Bettas are pretty simple and hardy, relatively easy to care for as long as you keep up your water changes as well as feed the appropriate amount of food. You might be able to breed them in a 5 gallon, but your gonna need a bigger tank like a 20 gallon to grow them out, once they reach of age and start fighting, buy one of those 30-40 gallon bins at Walmart with a heater and a sponge filter. Go to your hardware store or Home Depot and buy a material called egg crate, make sure the holes are small enough where the bettas can’t swim through and get to each other. Forge a dividing system that you can work with. Or save pickle jars.