Wiring
The breaker size is based on two things, how much you need, and how much your wiring can handle.You need a breaker that will handle all of the appliances you plan on using (including the charger), along with a little more, in case you add more later.In other words, you don't have to have appliances that draw a total of 15 amps, and use only a 10 amp breaker. If you do, it won't stay on when everything is running.That said, the purpose of the breaker is to ensure you don't have too much amperage going through your system. If you have a 20 amp breaker, and 15 amps worth of appliances, and wiring that can only safely hold 10 amps, you're going to have problems. When the wires get hot, the breaker won't break.That said, my recommendation would be that you make sure your wiring will handle 30 amps throughout, and then get a 30 amp breaker.