4 better, 6 or more best. You aren't going to be able to pick male from female. If you can I'll send you some angel pics, just got in 600some angels from a breeder, 23 are adults. I'll gladly provide pics.
Standard stocking is 10 gallons per adult angel, 5 per potential breeder size. Angels are cichlids, keep a divider handy, cichlid behavior can occur at the drop of a hat.