Tell me if I NEED a multisite installation to do this...

I have an educational site. I want different teachers to offer their own courses right on the site. I want everybody's courses to show up together when you click on the Courses tab. I'm trying out Marketpress.

I don't want each teacher to have their own "school" on my site...kind of like other group e-commerce sites where each user has their own "store". Which is what I think a multi-site would do.

So, I think I don't need a multisite.

But, I want each teacher to be able to enter in their own paypal address, and for me to pay them all (minus the site's fee) once a month.

So this part makes me think that maybe I do need a multisite?

Could somebody clear this up for me? I'd really like to avoid having a multisite. I'd rather it be just one site that a number of people contribute to...but get paid individually.

So this is really two questions:
1. Must I have a multisite installation to do this?
2. If I can just do this all in one site, how do teachers set their paypal addresses in Marketpress?
...Whoops, three questions!
3. And how do I set the site's percentage?

Thank you for all your help!!