Can a subscriber be charged an initial fee as well as have a recurring charge processed through authorize.net?
These charges would be based on the level of membership and each membership type would have a different registration form.
yes.
Authorize.net AIM+ARB are integrated and are both used for a subscription.
Different forms are possible as long as there is no mandatory field not on all plans (this is a small limit of CBSUbs 1.0.0 that should be lifted soon (priority item)).