Here is another idea. You will need a torch height control. Once you accept that as a design feature it becomes obvious that the torch needs to be raised and lowered by a DC motor driven by a power op-amp. This hugely simplifies the THC and greatly reduces the weight of the torch assembly which, in turn, greatly reduces the weight of the gantry needed to accelerate it. It also reduces the wiring and without electronics at the torch head it makes you immune to interference from the arc.
If you think of torch height as an obvious job for a DC motor it is not hard to get cut and pierce heights using micro-switches rather than using a computer and vast hardware to do something absurdly simple. There are more ways to kill a cat than building an Arnold Schwartznegger, terminator look alike, cat stomping machine.