I've seen installations with three gear hooked to one retract servo--not easy to setup, but it is possible. The steering will get you, though. I don't see anyway around a separate servo for that--pull pull is the only way I know of around it. I've not setup trike retracts, but I've done some main gear retracts--both pneumatic and mechanical. Pneumatic is definitely the easiest to setup, IMO, but you have to have room for the tank, and valve. This is sometimes difficult to find, but that looks like a fairly thick wing--put the airtank in the wing! If it isn't a scale plane (I don't know anything about the plane at hand), then I'd definitely change it to a tail dragger and be done with it!