How to deactivate payment for Pro Sites plugin

Hello,
I want to deactivate the payment for Pro Sites, and I may change site level manually for selected subsites. So
1. How to completely deactivate the payment of Pro Sites? or how to hide the payment for users?
2. I want to create several site levels, but seems I have to enter a price for each VIP level. How to create levels without a price?
3. I created 2 levels so far, but for some reason, any sub-site in the level 1 is blank when visited. What may cause this issue? What else should I pay serious attention when using Pro Sites to manage levels, based on your experience?

Regards
YZ