If you are ordering from V1, buy the kit and then add your extras. If you add additional timing belt at the same time as your kit , Ryan will just increase the length of belt he ships. He will ship a single length, not cut it for the extra. As for the “harness,” just add additional extension cables. You probably want to order five of them, one for each stepper motor.
I do have some concerns about your build. In terms of size, a 4’ by 4’ working area is at the outside edge of what I’ve seen on the forum for successful Primo builds. Many on the forum would encourage you to consider building a Lowrider instead for a build that size. As for the tubing, steel bearings on aluminum tubing, even with an anodized surface, is problematic in my mind. I cannot say it won’t work, but I’d have a backup plan. Or maybe start with a single pipe test piece and one of the trucks, and run the truck up and down the pipe for some time to see if there is an impact.
As for plasma, you may want to spend a bit of time researching on the forum and elsewhere before you place your order. I’ve just skimmed the topics, but there seems to be some special considerations when making an MPCNC into a plasma cutter. Getting the right torch and dealing with the electronic noise are two issues I’ve seen mentioned, and I’m sure there are others.
Thanks yea I have some of the same concerns. I will start at 4x4 if need be I will shrink.
I have done a far amount of reading on the plasma and yes I realise they can be problematic. Mine is not high frequency so at least I have that on my side.
My expectations are not super high if all else fails I should be able to get a laser engraver/cutter and router going.
A single mid-span is good enough for steel tubing. I had mid-span supports on my Burly (previous version of the MPCNC). They required me to drill a hole in the tubing. If you have any doubts (and if the mid-span supports you select require holes), you could just add a couple of extra holes in the tubing before assembly to make installing more supports later easy.