I think stranded servos will be fine. i have flown them on all sorts of glow planes that size for years on single elevator servo setup and never hand any issues i still think all this torque is over rated run them and you will be fine
Depends on what you are doing...
BTW, put your rudder servo up front, and you might want to consider a 2 stroke 61 or 91, that would be awesome, and much easier to run than a 4 banger.