Inputs & outputs & relays ohmic

Mount the divider inside the power source, THCAD outside of it and as far as you can given the conditions. It can be inside the electronics cabinet, but far from other electronics.
Having the divider outside the power source means having wires out that carry over 100V at 40 to 150A so a short there will make some nice fireworks.
THCAD should be mounted as Icelander did, that is the best solution, in a box somewhere in between.
As for the torch, it can not be done, meaning the straightening of the pipes, that would require removing a lot of hard plastic and the tubes are very brittle and break easily. You can just cut the hand holder part in half, that will make it much more manageable.
Oh and getting the voltage from the torch itself is never a good idea, that is where the 15000 to 20000V go to strike an arc. Voltage for the THC should be wired as close to the rectifier as possible or at the capacitor plate located nearby. That capacitor plate is what keeps the rectifier from blowing up every time the arc strikes.
This was as short as i could make it to make sense, hopefully.

I am the tech support for over 15 plasma cutters here, and some other machines, and the best thing is i get called very rarely, like really really rarely, maybe once every 2 to 3 months, even those calls get dealt with over the phone in under five minutes most times. That is a testament to the reliability of Linuxcnc.
Those are all machines that are used all day (7AM-8PM mind you) every day, not every Sunday though. Spring/Summer/Autumn there is no rest for them.
Mechanical issues get dealt with by their owners most of the time.