Guitar to Hammond tone wheel control interface
You will (or may be) surprised to know that the problems of detecting the individual strings from a normal geetar pick-up is problematic. You either need a bank of individual filters set to semi-tones across the full range (that's nearly 3.5 octaves or 58 semitones) or you use a powerful microcontroller.

A good start is to get hold of individual inductive proximity sensors and have one for each string. Now you split the problem into more manageable blocks and what I've done (in the past) is use a high gain clipper for each of the 6 outputs. This gives virtually a square wave output similar to the tone wheel sound. Mix the square waves together and you turn your geetar into an organ (and I've got old tapes to prove that).

If you are intent on using the hammod tone wheel then good luck but, you might be missing just how complex and slow it is to make filters to detect a single frequency on a geetar.