Unless you want to do massive water changes each day, a pair (male and female or two females) would be best. I have 7 fish in a 55 and it is a lot of work. Get large adult fish as they are much less likely to get diseases. I know this will sound strange, but it is cheaper in the long run to purchase expensive healthy adult fish than lots of small ones for less money.
My other comment is don’t mix colours. Fish of the same colour look better together - if you like red get two reds, if you like blue get two blues etc.
Matt