Blimp:
To scale down bit (no pun intended) use the two motor idea for steering, one on forward and one on reverse channel (I think you could mod the remote with an extra button to fire both at once pretty easy) and the us the coils to control the pitch of an elevator maybe? Or better if you manage to get the steering channel to drive a motor, mount a third vertically for altitude control. Then you only need one bit, and two hands to fly?
I was working on the idea of scratch building a blimp a while back (before I met the bits) and while possible, there are a lot of little details to work out.
Oh and the helium is far from cheap!
Planes:
Some of us have been talking these over already:
http://tinyrc.com/forums/showthread....&threadid=4693
Copter:
I think I have seen a small RC that got away without a tail rotor by just using a large flat fine. The air resistance was enough to counter the reaction forces from the main rotor.
The Real problem with helicopters is how complicated it is to get them to move, There are a lot of forces and odd pyhsical laws involved when you get a big blade spinning fast enough to lift something....