Partners registration on Marketpress?

Hi there

I am building a website just like Amazon or Ebay, etc...where producers, sellers will sell their items trough my website for a small procentage!
My question is: How can I Set up a registration for THEM, so after they log in, they will be able to see ONLY the MarketPress Procuct Settings( add product, manage orders, set up payments, shipping, etc), but NOTHING else( no any other admin authorization for them)??? Is there an extra plugin for this? How can I restrict them to see only the MarketPress settings, but not the theme settings for example?
I really appreciate any help.
Thank You