I have never bred finches, however I used to work in a pet store where we kept several in one cage.... the number was always odd or even since people were always buying them.
What I noticed was that certain ones nested while others kind of "did their thing." There was never any fighting due to the number. Finches don't really develop feelings of jealousy, normally.
So as long as you have the sexes figured out, you should be good to go. It's kind of hard to breed finches if you're inexperienced but if you know what you're doing, best wishes.