How does marketpress handle accounts

Hello,
I have a main network site and will eventually have several ecommerce sites linked through a multisite to this network. I am curious about site accounts for site owners and accounts for those who purchase items on these sites.
1) Is it necessary to have a buddy press in order for people to have accounts to buy, or is this simply a social networking add on which isnt necessary for marketpress to run?

2) If i have an account sign-in on my page, this will be for site-owners to access and make changes to their site?
3)how do i handle those that do not own a site through my network but are interested in buying on the network...how will i show their history of purchases and keep their account info for them to use later? Is this a separate plugin or is this part of marketpress?

Thanks any help i can get wrapping my brain around this will be much appreciated.

Kate