Payment processing, legal overhead

Hello, I'm a developer running a site by myself. I'm considering adding a feature which allows visitors to pay for services from other visitors. I would like to do this incurring minimal legal cost and minimal operational cost. I would write the software which does payment/order processing , have the money transferred to my account, and cut monthly checks to people who made money.

1) How much legal overhead is involved in providing such a service, and what legal issues should I expect to face?

2) Would this be classified as a money transfer service, like tipjoy is? (http://tipjoy.com/faq/#q8)

3) Is it reasonable for one person to pull this off? Why/why not?

Any information would be helpful, I'm just brainstorming at this point.