From what I understand, 6 pairings of a mature, breeding sized male is 'standard'. I'm sure you could get more or less either direction depending on many different variables including age, size, etc.
Personally, the most I've paired any male was 5. Can't comment on fertilization as I had a range of females from mature to first timers. It was my first year breeding as well.
Since, I have usually bred each male a max of 4 times. I have personally noticed within my breedings that first time, unbrumated males have tended to be less fertile.
D80