Hey droople, welcome aboard. What you're looking for isn't a mainstream need, so we don't have that worked into core. However, something you can do that should work great in the long run but require a little more work up front is the following...

• Have the main site still be the registration site w/ links to the artist pages.
• When an artist gets approved, actually create a new site on the same Drupal install using a custom install profile.
• Don't give your artists full admin access (i.e. user 1), but in your install profile actually setup most of the site for them but give them full store access.
• Let them administer their own stores that way.

With Drupal you can setup as many sites on one install of Drupal as you want, and I think this is the way to go. Right now there's no way to have individual PayPal accounts like you're looking for. You could always have artists sign up w/ the PayPal account they want to be paid to and disburse the funds yourself.