For the motors, look at alliedelec.com they have good motors at a reasonable price. I suggest looking at the ones put out by Globe Motors. As for mounting an encoder to a motor without a back shaft, look at US Digital. They have a small encoder (E4P) for about 20 bucks. If the motor shaft is long enough this encoder will mount between the motor and the pulley or gear you put on the motor. If not, the way I did it, is that my motor shaft did not go all the way through the pulley, so I put a coupling inside the rest of the pulley and bought an aluminum shaft (that fit the coupling), cut it to size and put it through the other side of the pulley (basically extending the motor shaft) and mounted the encoder on the end of it.