ooooh, you have lots of stuff there and an interesting project. draw bars are available at most of the tooling suppliers like Enco. Belts are just industrial belts, how are the bearings at the idler pulley ? now is the time to change them if needed.
as far as your power switch, the vfd cannot be switched between the vfd and the motor. I low voltage power relay would be a good idea, or if your vfd has a connection for a remote switch for on / off and forward / reverse, that would be the way to fly.
what is the quill fit ? R-8 ? or what is the options on that machine.
I believe im a distributor for Jet Tools so if your trying to find a source maybe I can help. I'd need to call Jet to confirm im still listed.
the round column clamping system must be tightened and retightened to keep it from moving when your milling. just a thing to remember or you will get some odd results
Jet is not very friendly with their prices so I would advise trying aftermarket / Evilbay etc first. . .
good luck with your project,
davidh