Will this affect my income in any way for the home game later in the season?
I think for this game the visitor income would slightly less, because of the fan mood of the opponent.
And for your team, you got a sure win against your rival, and i don't think that they rate him less but i have no experience with it(but i would be quite sure you get 4,5+ Balls there).
Is it based on number of players? Starters vs Backups?
Starter get 36 minutes
Backups 10min
Reserve two minutes
open spot won't be devided to the other players, so the minutes there are just missing
If you combine starter and Backup you will loose 5 minutes so i wouldn't recommend it(at least on the training spot, for gameshape it might be useful). But you could combine reserve with anything you want(even multiple) without getting biased through it.
I don't know what happen if you lineup a player at 2 or backup spots, this might work with full minutes or not.