I've sort of defaulted to 8, figuring if the average games goes about 8 turns, carrying any more than that doesn't really help you. Carrying less could leave you with a wasted resource.
Is this what you do? I find a common problem is if i have three free reports and three card draws a turn, i'm depending on luck to get me at least 1 card that can go to all three free reports. i suppose when this happens is when i need to burn a card play on kivas of masaka to refresh and make sure i have the cards i need? I.E. maybe i don't need more than 8 free reports, i just need more card draws?