JG,
How I would attack it..
1) The collective head: any way you can think of (real life, electronics box with switches, whatever).
2) Linkage to rotation point: How solid do you want it to be? You can make it pretty solid with PVC piping and such (talk to BIGNEWY). I would use metal piping with ballbearings for rotation.
3) Tension: That I'd have to think about and is dependant on the actual mechanics that you decided to build.
4) In terms of interfacing it's so easy, as you say: leo bodnar board. Get a potmeter (or better a hall sensor).
One way of keeping the collective in place:
Gas spring.
Hope this can get you up to speed.