Hi!

Male bettas are fighters. You can ONLY HAVE ONE in a tank. If you get 2 and put them together, they will fight to the death. It is OK if you use a tank separator, as then it is as if they each are the only one. They can't reach each other. the separator should be solid so they can't even see each other.

Bettas do not need a lot of space. A 5 gallon tank should be OK if you are not putting any other fish in there. But if you are going to get a filter, heater, etc, most folks go for the 10 gallon and add a few other community fish.

Most male bettas do fine in a community tank with other fish. However, the fish are like humans, individuals. So I have had 5 male bettas at different times. ONE did attack the other fish and I returned him the next day.

Female bettas are not quite as showy as the males. but you can keep as many of those together as you want.

Hope this helps!