Additional line-height (I went all the way to 1.9) would really give your site much more breath and feel lighter and more welcoming.
The weight of the button typography doesn't balance well with the thin line around. Even bringing it down to 600 feels much more balanced.
There isn't a ton of contrast between the h3's and the body copy. The uppercase also causes a lot of tension for me when reading. When I removed the uppercasing and the override media query (so camel case and 1.25rem) it was already feeling better.