After some time away from the workshop I have finally got some info to report back with.

OK first off one by one I rewired the motors in parallel and set the amps/phase according to the chart given for the motor after that I tuned them all upto remove the resonanse issues. Now they sit idle and are much quieter and I'm now confident that their torque is much more suited to my setup. I tried a cut at 5mm deep in Trespa (HPL) at 3000mm/min without any problems other than the expected noise from the cutter. It didn't skip a step and the final part was as expected.

As for the dust boot I tried the 3d printed skirts in PLA but if you're thinking of replicating it I'd say don't bother, it didn't work. PLA might be stiff but it's still too brittle, maybe another material might work but mine went into the bin. I work in a business that does plastic fabrication so had a decent offcut of clear flexible PVC sheet, the sort you see hanging on doorways. I ended up using that with 8mm strips cut in to act like the bristles would have done. It works well enough but I'd still say bristles would be better but maybe I'll do that at a later date with some 0.15mm paintbrush bristles.

If anyone is interested the machine allegedly pulls just over 3 amps from the socket which is slightly confusing given the amps being pulled by the spindle on the VFD is showing as 3.3a. All devices were powered from the same socket so that might need a bit of investigating. Without the spindle running it shows 2.3a when all 4 motors are running at rapid speeds.

So all issues are now resolved, for now. There will be more to follow no doubt but until they show up I'd like to thank everyone for their help and assistance on the all of the above.