I've only worked on the API so you should check this with someone else too, but here's my answers:
Sounds good to me, as long as it makes sense in the UI.
Yes
We decided to not have different user roles, so the idea is that all contributors should have access to both read&write operations. So no need to display them. The only distinction we make is that if you are the creator of the list you also have the ability to invite and kick out other collaborators.
As a User, I want to see which shared shopping lists by others users I have access to
(OLD: As a user I want to be able to see all shoppinglists I have created and all other shoppinglists that I have access to)
Questions: