I told you you can make fees off parent clubs, and you definitely can. And unless it's been changed this year, I'm pretty sure you can have more than 1 parent club.
a) I don't know if it's strictly once a season, but if they just told you they couldn't find a club, I'm sure they won't take another request for a while
b) Chances are, you're more likely to get a parent club in the next league up, but I've seen clubs with parent clubs that are 2 leagues above them (mine did too when I started there)
c) You play a bigger team, the fans are willing to pay more money, so you get more ticket revenue. But bigger teams alsp demand more participation fee, if you will, for playing in that friendly. All I was saying, is don't only look at the revenue increase, but also factor in the higher fee you have to pay, so that you can decide based on the net profit (ticket revenue less the fee)