It depends mostly on the motors you want to use. Every motor got a sheet with certain props tested. So you can see how much it pulled at 25%, 50%, 75% and 100% throttle with a certain prop. You will need an ESC which can offer more than the motors need. E.g. if a motor pulls 45amps at 100% I would use an ESC which can offer 50 or maybe even 60 continued.