Hi,
For a model of that size i would think 1 805 would be enough. My Dads used them on one of his models and have performed very well, we've got 2 lots of 2 servos on 1 surface.
I would strongly advise (i think Hitec tell you this anyway but...)you run them from the battery packs directly otherwise you could burn the RX out as they draw a HUGE amount of current!
Have fun