If you go by the 7 watts/ounce rule, and leave yourself 20% worth of charge at the end of the flight, then you've got enough battery for a 28 ounce plane.
It's probably better to plan on 25oz, so it can get a bit heavier during the build and during any repairs.
That's really, really light for a Ringmaster. I'm not sure just what would come out to that weight, but that's what you want to aim for.