Permanent Subscriptions

[Cable_Player]

Hi there,
I've been searching around and can't find anything that jumps out at me, so here goes:

I'd like to be able to do two things with the Paid Subscriptions in vB4.

1) When a member purchases a specific subscription it lasts forever, there is effectively no renewal.

2) Limit how many of a specific Paid Subscription can be purchased.

The reason for this is because I want to offer different incentives for each paid subscription. You could use kickstarter for an example with how each project is backed and the more you pay the more you benefit from, but only X amount of each option is available.

Does anybody know how to achieve this?

Thanks.