People typically use a 480-900 or so mAh Lipo with regulator. The battery size depends on personal preference, as well as if the airplane will be close to weight or not. There is little to no vibration, so you're not using too many mAh per flight, around 50. I think I'm using around 125 per flight for a YS 1.70 powered model, and was using 225 per flight with the CDI.

I will likely use dual 480 Lipos with Tech Aero regulators, as I've had good luck with them.

You couldn't pay me to use a BEC on a 2 meter airplane. Not only would I hate to lose the airplane for monitary reasons, but that would be pretty dangerous if something that size with large Lipos for the motor went in somwhere populated.