I don't x ray my girls... they will, or they won't be pregnant, and knowing ahead of time how many doesn't change anything. I don't take deposits until I have LIVE pups on the ground (and they have been alive at least 3 days.. accidents happen!)
Size of litters is a fascinating topic. I try to choose females for breeding that came from large litters, whose mothers were able to successfully carry, whelp, and take care of all her pups, and who are regular in their heat cycles. With all that, though, I haven't been able to predict litter size at all. And, believe it or not, it's harder to have a litter of many pups all survive, than a medium litter of 5 -7. So, we wait!