jbot

I have just purchased an ARF H/L Scorpio Supermarine Spitfire. I have run various power plant possibilities through the MotoCalc program and one interesting possibility is a Kontronik Tango 45-05 motor coupled with a Sanyo CP-1300 21 cell pack with a 10x5 prop. This combination weight of 47.9 oz. (14 oz. est. plane weight, the rest in batt and motor + esc.) and gives performance figures of:
Thrust = 52.9 oz.
PSpd = 53.7 mph
RofC = 1392 fpm
Time = 4 min 09 sec
Batt and motor amps = 15.9
Input W = 360.9
Input W/lb = 134.6
Loss (W) = 31.5
MgbOut (W) = 329.4
Outpld (W/lb) = 110.1
MotGb Ef (%) = 91.3
Shaft Ef (%) = 82.1

This is my first effort in trying to modify an existing powerplant suggestion in an ARF kit. My questions are:
1. Is this engine/batt/prop combination a reasonable combination for this airframe? Conventional wisdom seems to indicate that the airframe should be appx. 1/2 the weight of the finished product? Why?
2. Kontronik seems to be the most efficient setup. Where can I purchase the necessary motor and accessory parts for installation? Is there a hobby shop which carries Kontronik products?
3. Any other comments which I might have missed.
4. I need help!! Come on guys, give me some guidance here!

Best Wishes,
Jim Bottom