On the cable, have you considered hot glue? Most of it has a melting point well above 100c, so it should be fine in chamber. Especially if all it’s doing is keeping some wires in place. I’m using a PCB xy endstop, so I don’t have a lot of advice to give here :(

On klicky, I’ve had quad gantry level fail a few times as you’ve described, but it was always a mechanical issue. The first go round I didn’t attempt to manually level after assembly and I guess it was too far out of level. I manually leveled somewhat square to the frame and it succeeded on the second attempt. The other times it failed were when I didn’t have the ptfe tube installed and the spool fell off its holder and caused misstepping. Have you ever had a successful level?

Finally, on the spool holder. I am using a holder with bearing, but it was designed to sit on top of an I3 clone. There’s not really a spot for it on the voron, so it’s currently sitting on my desk. I finally figured out how to get the ptfe tube to feed from it, which has helped. The thing I’m running into is that the polymaker 3 kg spools are too wide for the holder, causing friction between the spool and the bolder itself. I’ve run a couple of other companies 3 kg spools on this holder before and it was never a problem. Then again, none of them were this wide. I’ll have to measure the spool to see if it fits this holder.