I am confused by whether I want the Pro Sites plugin,

I am confused by whether I want the Pro Sites plugin, Membership, or Both. It is a buddypress, and maybe multisite but I dont think that will be necessary at this stage.

Here is what I am trying to accomplish:
The basic premise of the site will be an art competition, where users can upload their art for review by peers and experts.

There are 3 levels of accounts:
User (free, open to anyone, able to provide a simple score other people's art (like/dislike) but no ability to upload own art or leave comments on other's art)
Artist - paid, able to upload video/pictures of their art, comment on the work of other artists, and score art on a more complex rating system than "Users"
Ambassador - paid at different level, able to upload art access to finalists based on User and Artist Reviews,. unrestricted ability to comment, etc otherwise

Memberships seems to be oriented to restricting access to content, not necessarily functions. ProSites seems to control access to some functions, though the scope of them seems to be pre-defined for a site like edublogs, not necessarily the types of features I listed above.

I hope that makes sense.