So there is a lot of things in 5e that would not fit very well into a GW1 themed version but also a lot of things in GW1 that just either are too complicated to merge over or would not fit. So I have some suggestions as paths to take for this that do not change much but still try and hold true to both. I will state the difference between official, and what will be changing.
Armor
Armor Proficiency: If you wear armor that you lack proficiency with, you have disadvantage on any ability check, saving throw, or Attack roll that involves Strength or Dexterity, and you can’t cast Spells (taken from official armor page).
Armor Class (AC): Armor protects its wearer from attacks. The armor (and shield) you wear determines your base Armor Class (taken from official armor page).
Stealth: If the Armor table shows “Disadvantage” in the Stealth column, the wearer has disadvantage on Dexterity (Stealth) checks (taken from official armor page).
Shields: A Shield can made from wood or metal and even of different qualities. They are carried in one hand, and you can benefit from only one Shield at a time. Wielding a Shield increases your Armor Class depending on which kind equipped (changed from a base 2 to having different tiers, check charts below).
Light Armor
If you wear Light Armor, you add your Dexterity modifier to the base number from your armor type to determine your Armor Class (taken from official armor page).
Cloth: Cloth Armor is resemblent of normal clothing (new weaker tier of padded but still light).
Padded: Padded Armor consists of quilted layers of cloth and batting (taken from official armor page).
Medium Armor
Medium Armor offers more Protection than Light Armor, but it can also impair Movement. If you wear Medium Armor, you add your Dexterity modifier to the base number from your armor type to determine your Armor Class, sometimes having a cap of +3 (mostly taken from the official page, but removed a permanent cap of +2 and instead only added some materials to be +3 cap).
Leather: The Breastplate and shoulder protectors of this armor are made of leather that has been stiffened by being boiled in oil. The rest of the armor is made of softer and more flexible materials (taken from official armor page).
Studded Leather: Made from tough but flexible leather, studded leather is reinforced with close-set rivets or spikes (taken from official armor page).
Hide: This crude armor consists of thick furs and pelts. (taken from official armor page).
Scale/Bone Mail: This armor consists of a coat and leggings (and perhaps a separate skirt) of leather covered with overlapping pieces of metal or bone. The suit includes gauntlets. (taken from official armor page, except added bone).
Heavy Armor
Heavier armor interferes with the wearer’s ability to move quickly, stealthily, and freely. If the Armor table shows “Str 13” or “Str 15” in the Strength column for an armor type, the armor reduces the wearer’s speed by 10 feet unless the wearer has a Strength score equal to or higher than the listed score. Only proficient warriors can manage their weight and bulk. Heavy Armor doesn’t let you add your Dexterity modifier to your Armor Class, but it also doesn’t penalize you if your Dexterity modifier is negative. (taken from official armor page).
Chain Mail: Made of interlocking metal rings, Chain Mail includes a layer of quilted fabric worn underneath the mail to prevent chafing and to cushion the impact of blows. The suit includes gunatlets, heavy leather boots, and an open helmet as well (taken from official armor page, slight change to description as this needs to be better than chain mail but worse than full plate).
Half Plate Mail: Half plate consists of shaped metal plates that cover most of the wearer’s body, head to toe. Leather is usually worn underneath and is what holds the plates.
Full Plate Mail: Full Plate consists of shaped, interlocking metal plates to cover the entire body. A suit of plate includes gauntlets, heavy leather boots, a visored helmet, and thick layers of padding underneath the armor. Buckles and straps distribute the weight over the body (taken from official armor page but changed to full plate name).
Shields
Wood Shield: A small wooden shield that does not weigh much and can be used to block lighter attacks.
Leather Shield: A larger, more thick shield, with a coat of leather over it to be able to take more impacts.
Metal Shield: A large heavy metal shield that can block almost anything.
Armor Chart
All armor here is mainly taken from the official page style wise with a lot of changes throughout. All is subject to big changes, such as wanting to add specific armor sets.
Light Armor:
Cloth / 11 AC + Dex Mod / 1 lbs.
Padded / 12 AC + Dex Mod / Disadvantage / 3 lbs.
Medium Armor:
Leather / 12 AC + Dex Mod / 9 lbs.
Studded Leather / 13 AC + Dex Mod / 13 lbs.
Hide / 14 AC + Dex Mod (max +3) / Disadvantage / 15 lbs.
Scale/Bone Mail / 15 AC + Dex Mod (max +3) / Disadvantage / 20 lbs.
Heavy Armor:
Chain Mail / 750 gold / 16 AC / Strength 13 / Disadvantage / 55 lbs.
Half Plate Mail / 1,200 gold / 18 AC / Strength 14 / Disadvantage / 60 lbs.
Full Plate Mail / 1,500 gold / 20 AC / Strength 15 / Disadvantage / 65 lbs.
Shield Chart
Shields:
Wooden Shield / 10 gold / +1 AC / 3 lbs.
Leather Shield / 15 gold / +2 AC / 6 lbs.
Metal Shield / 20 gold / +3 AC / 10 lbs.
Don and Doffing
The time it takes to don or doff armor depends on the armor’s category.
Don: This is the time it takes to put on armor. You benefit from the armor’s AC only if you take the full time to don the suit of armor.
Doff: This is the time it takes to take off armor. If you have help, reduce this time by half.
(taken from official armor page, increase medium doffing to 2).
Weapons
Weapons can be handled a few ways. Specific weapon proficiency just for damage alone, and have weapons with mods like in GW1, or have 2 proficiencies, one for weapon damage, and one for weapon effects (mods). This way a class could use a weapon they are not proficient in for damage, but it gives special mods that are useful. Or, allow all weapons to have mods regardless of proficiency and not have them restricted to weapon type like in GW1.
(Currently fleshing out the idea more, will update once it is delved into more with others)
So there is a lot of things in 5e that would not fit very well into a GW1 themed version but also a lot of things in GW1 that just either are too complicated to merge over or would not fit. So I have some suggestions as paths to take for this that do not change much but still try and hold true to both. I will state the difference between official, and what will be changing.
Armor
Armor Proficiency: If you wear armor that you lack proficiency with, you have disadvantage on any ability check, saving throw, or Attack roll that involves Strength or Dexterity, and you can’t cast Spells (taken from official armor page).
Armor Class (AC): Armor protects its wearer from attacks. The armor (and shield) you wear determines your base Armor Class (taken from official armor page).
Stealth: If the Armor table shows “Disadvantage” in the Stealth column, the wearer has disadvantage on Dexterity (Stealth) checks (taken from official armor page).
Shields: A Shield can made from wood or metal and even of different qualities. They are carried in one hand, and you can benefit from only one Shield at a time. Wielding a Shield increases your Armor Class depending on which kind equipped (changed from a base 2 to having different tiers, check charts below).
Light Armor
If you wear Light Armor, you add your Dexterity modifier to the base number from your armor type to determine your Armor Class (taken from official armor page).
Cloth: Cloth Armor is resemblent of normal clothing (new weaker tier of padded but still light).
Padded: Padded Armor consists of quilted layers of cloth and batting (taken from official armor page).
Medium Armor
Medium Armor offers more Protection than Light Armor, but it can also impair Movement. If you wear Medium Armor, you add your Dexterity modifier to the base number from your armor type to determine your Armor Class, sometimes having a cap of +3 (mostly taken from the official page, but removed a permanent cap of +2 and instead only added some materials to be +3 cap).
Leather: The Breastplate and shoulder protectors of this armor are made of leather that has been stiffened by being boiled in oil. The rest of the armor is made of softer and more flexible materials (taken from official armor page).
Studded Leather: Made from tough but flexible leather, studded leather is reinforced with close-set rivets or spikes (taken from official armor page).
Hide: This crude armor consists of thick furs and pelts. (taken from official armor page).
Scale/Bone Mail: This armor consists of a coat and leggings (and perhaps a separate skirt) of leather covered with overlapping pieces of metal or bone. The suit includes gauntlets. (taken from official armor page, except added bone).
Heavy Armor
Heavier armor interferes with the wearer’s ability to move quickly, stealthily, and freely. If the Armor table shows “Str 13” or “Str 15” in the Strength column for an armor type, the armor reduces the wearer’s speed by 10 feet unless the wearer has a Strength score equal to or higher than the listed score. Only proficient warriors can manage their weight and bulk. Heavy Armor doesn’t let you add your Dexterity modifier to your Armor Class, but it also doesn’t penalize you if your Dexterity modifier is negative. (taken from official armor page).
Chain Mail: Made of interlocking metal rings, Chain Mail includes a layer of quilted fabric worn underneath the mail to prevent chafing and to cushion the impact of blows. The suit includes gunatlets, heavy leather boots, and an open helmet as well (taken from official armor page, slight change to description as this needs to be better than chain mail but worse than full plate).
Half Plate Mail: Half plate consists of shaped metal plates that cover most of the wearer’s body, head to toe. Leather is usually worn underneath and is what holds the plates.
Full Plate Mail: Full Plate consists of shaped, interlocking metal plates to cover the entire body. A suit of plate includes gauntlets, heavy leather boots, a visored helmet, and thick layers of padding underneath the armor. Buckles and straps distribute the weight over the body (taken from official armor page but changed to full plate name).
Shields
Wood Shield: A small wooden shield that does not weigh much and can be used to block lighter attacks.
Leather Shield: A larger, more thick shield, with a coat of leather over it to be able to take more impacts.
Metal Shield: A large heavy metal shield that can block almost anything.
Armor Chart
All armor here is mainly taken from the official page style wise with a lot of changes throughout. All is subject to big changes, such as wanting to add specific armor sets.
Light Armor: Cloth / 11 AC + Dex Mod / 1 lbs. Padded / 12 AC + Dex Mod / Disadvantage / 3 lbs.
Medium Armor: Leather / 12 AC + Dex Mod / 9 lbs. Studded Leather / 13 AC + Dex Mod / 13 lbs. Hide / 14 AC + Dex Mod (max +3) / Disadvantage / 15 lbs. Scale/Bone Mail / 15 AC + Dex Mod (max +3) / Disadvantage / 20 lbs.
Heavy Armor: Chain Mail / 750 gold / 16 AC / Strength 13 / Disadvantage / 55 lbs. Half Plate Mail / 1,200 gold / 18 AC / Strength 14 / Disadvantage / 60 lbs. Full Plate Mail / 1,500 gold / 20 AC / Strength 15 / Disadvantage / 65 lbs.
Shield Chart
Shields: Wooden Shield / 10 gold / +1 AC / 3 lbs. Leather Shield / 15 gold / +2 AC / 6 lbs. Metal Shield / 20 gold / +3 AC / 10 lbs.
Don and Doffing
The time it takes to don or doff armor depends on the armor’s category.
Don: This is the time it takes to put on armor. You benefit from the armor’s AC only if you take the full time to don the suit of armor.
Doff: This is the time it takes to take off armor. If you have help, reduce this time by half.
Light Armor | 1 minute | 1 minute Medium Armor | 5 minutes | 2 minutes Heavy Armor | 10 minutes | 5 minutes Shield | 1 action | 1 action
(taken from official armor page, increase medium doffing to 2).
Weapons
Weapons can be handled a few ways. Specific weapon proficiency just for damage alone, and have weapons with mods like in GW1, or have 2 proficiencies, one for weapon damage, and one for weapon effects (mods). This way a class could use a weapon they are not proficient in for damage, but it gives special mods that are useful. Or, allow all weapons to have mods regardless of proficiency and not have them restricted to weapon type like in GW1.
(Currently fleshing out the idea more, will update once it is delved into more with others)