This is fun!
Use theme control center & categories.
With theme control center, you can assign a distinct theme to each artist. (Which is very cool!)
You can assign permissions to categories. Give Anonymous "view category" and that artist's group "admin category". (And put artist's editor in that group)
When a page is created, make sure to save it with the right category, so it gets the theme and the permissions.
About the menu: there are different ways to approach this. Show me the current site (or how you want it to look) and I will suggest something. You could use menu generator or menu page module.
Cool thing with Tiki: Each artist could have a blog, a discussion forum, calendar, etc