This is a very good question.
The best guitar for a Gizmotron is one with a 25.5" scale. This is because the Gizmotron wheels need to contact the strings around the 24.25" mark for the wheels to produce a smooth sound. If the wheels are located less than 24.25" away from the nut, the wheels will be choppy, especially on the higher frets of the higher strings. On something like a strat, the wheels can be located even further back, and the sound will be even smoother. This is why we recommend locating the wheels as close to the saddles as possible. Get as far back as you can.
For pickups, you can pretty much use anything, but humbuckers or noise-canceling single coils are recommended. A P90 pickup in the bridge position will likely pick up the hum of the Gizmotron motor. If you have a guitar with a P90, you want the Chrome Gizmotron, as it is metal and has superior motor noise shielding over the black or clear models.
If you are looking to emulate real strings, the best thing to do is treat the gizmo guitar like an acoustic and plug directly into a mixer. Guitar amps add far too much color and aren't capable of reproducing the full frequency spectrum that the Gizmotron wheels can produce.
Hope this helps.