I'd have to agree that the number of posts (500/1000) is way too low. I'd rather see something like 1,250/2500.
I'd have a free membership that would have limited access to the number of forums:
Free membership = 3 forums (etc etc, celebrity and relationship) for example.
Paid membership gets access to all forums immediately and PM's. Premium membership gets to all forums, chat, PM's and all galleries.
Tossing out numbers here, let's say that a paid membership is $7.50 a month that's like 2 cups of coffee at Starbucks per month and premium membership is $11.00 a month that's less than a Pizza Hut Special per month.
Once someone gets to the required level, whatever you choose to set it at (I think the 500/1000 IS to low) then they can get 50% off once they hit the first level (3.75 a month for paid membership and 5.50 for premium) and an additional 25% once they hit the next level (1.88 for paid and 2.75 for premium). If someone pays annually, they get 10% off. Then when they hit the required level and pay annually they get 60% off the first level and then an additional 35% off the next level.
For the free memberships, once they hit the required amount of posts they can get the discounts if they want to become paying members. For the free memberships, I'd give them an opportunity, once a month, to vary which forums they can get access too. Or, if you want, free memberships get access to all forums but no galleries, no chat and no PM's for one month. Then, after the one month, they can decide which forums they want access too and that can change on a monthly basis.
Finally, I think you undercharge for the service that you provide. I think a reasonable price, that you determine would bring a better value to the product. On the flip side, as part of the TOS, if a person is banned they get no refund of monies and I would make the reason for the ban public.
Thanks,
Sklar