I'm looking for similar solution, but I'm not sure this is what I need.
1. I want to limit author with memberships, but to leave content free for all visitors....
2. I would like author to have free of charge publishing for 3 months
3. I want to be able to confirm payment from backed (in case they paid by bank transfer)
4. Also, is the registration page customization ready? (I need some more fields to be entered from authors)