The most generally accepted size tank/bowl for a betta is 1 gallon minimum. The smaller the tank the more water changes you have to do so that is something to consider. It is also generally accepted that males should be kept alone. Having said that, I have successfully kept male bettas with ghost shrimp, snails, corys and whiteclouds but it depends on your set up, the fishes personalities and if you are willing to take the risk (it is a risk). Of late, I have decided it isn't worth the risk and the tank that my male betta Wraith shares with the cherry barbs is divided so they can't mix. The rest of them have their own tanks from 1 to 3 gallons in size. All of them happy and healthy.