Ask some functions in Pro version

We are using S2member free version now and plan to change to the pro version. However, we are not sure that the pro version can do all we want or not. We listed our main goals in the below. If Pro version don’t have these functions, is it easy for a web developer (begin level in PHP) to modify a code after a purchase? Or should we buy the pro version then hire a freelancer to do like you recommend in pre-sale questions?
Thank you!

1. Two kinds of main member: sellers and buyers.
2. Both sellers and buyers will have membership levels depend on their selling.
3. Once a member registered as a buyer, they can also register as a seller.
4. Create member fields which can only be modified or viewed by administers
5. (Optional) Sellers could mange and check their products