Customer groups - price reduction + set number of downloads

[mykind]

Hello,

I would like to make some changes as to be able to set a limited number of purchased products on customer groups, along with the price reduction parameter (all my products are downloadable; I am selling subscriptions with a certain number of downloads included and now I have to manually check to see if a customer has reached their quota; I would like to set that automatically from the beginning). Does any of you know how I could do this? Is there a module I could use? What changes should I make and to what code?

Thanks!