XF 1.1 Paid Board Setup / User Upgrade Challenges

I would like to set my board up as follows:

New Users must validate their e-mail. When complete, they are automatically "registered" which only allows them to view content.

To post, users must upgrade for a 1x fee of $1.00 for permanent membership (MEMBER).

I also want a higher level membership with additional privileges which renews annually.

Challenge - I have 2500 users. I want to grand father in users that have at least 15 posts.

My first run at this I initially used an SQL statement to change every user with 15 posts or more User Group ID to the new MEMBER Group (which was 9). I had that user group to full rights but for some reason, those users lost ability to post or reply. So I reverted them back to 2 (REGISTERED) and changed the privs back to allow posting etc and things were fixed.

Any feedback? I think the biggest challenge here is the grandfathering old users.