I am hoping someone else will come in with some advice for Tye. I do not claim to be the great fund of all knowledge on the subject of autogyros! Working alone here I must admit I have never seen any other autogyros in flight - only my own! However here are some of my thoughts, but I will say the we all have differing approaches to the subject and my thoughts may not fit in with everybody.
Anyway - 50 inch diameter rotors, in my experience a .46 motor is on the `hot` side.
One of my planes is powered by an O.S. 40FP and has a 56.5 inch rotor disc. I consider it to be rather overpowered. Autogyros are great for slow flight, they are not speedy racers.
My smallest is .15 powered with 35 inch diameter rotor disc, and handles stiff breezes fine.
Weight is important, 5 ounces per square foot is maximum (I reckon), my .40 plane has only 3.5 oz loading. Try to keep your plane light. Are you going to have no moving surfaces on the tailplane? Dc is OK, but is requires a more complicated rotor head. Load on servo is cconsiderable too.
Colin