Hi ATC_RC and welcome back!
I'll use a ZDZ-40 gas engine.
I read somewhere, that 120 class engine will pull it around in a Piper Cub like style, so no aerobatics or almost no aerobatics will be possible.
Regarding servos: I'll use a cheap and very good Graupner C5077 servos, whose are 5kg/cm with 4.8V it's ab. 70 Oz
They're cost ab 15-17 Eur (ab. 20$)