Actualy a .010 or .020 is plenty of motor the the little Buttercup. I built one and flew it with a TD.020 rudder/elevator no throttle and a Cannon super micro radio. This little plane would do rolls, loops and the neatist little Lamchevoc (SP) I have ever seen. Flew from a school parking lot and never landed more than a few feet away. Not so sure about scaling this up though as it would need a lot of engineering. Very stable little plane built per plans.
Keep us posted with a build thread if you decide to do this!

JEB