CG Ultimate 2-stoke advice
I love my CG Ultimate, have been flying it for about 6 months now. Mine is powered by a YS 120 FZ, plenty of power there, but a heavy engine. AUW is just under 10lb, with nearly another lb of fuel to feed the engine.
For 2 strokes, it depends on the type of flying you want to do. OS 91 FX is a minimum, a good 108 should be aerobatic, and 120 should give you "unlimited vertical". Remember you also have a lot of drag - it is effectively 110 inches of wingspan to pull through the air.
You also need reliability, as with most bipes it doesn't glide. I know, I have a flattened undercart to prove it!
Other tips: as mentioned watch the CofG and weight of the engine. I kept one of the cut outs from the underneath of the fuz and used it to make a hatch under the pilot for the radio gear. Rudder servo is under the stab. Still needed 4oz of lead to balance.
If you can, build some right thrust into the firewall. I wish I had.