Thanks @Phaedrux and @grizewald for your comments. Re z drive, I will use a single NEMA 23. I have received the V-Core 3 screw upgrade. They originally use it with 3 NEMA 17 and also suggest to drive them independent for bed levelling. I have decided against that. I have received my trust bearings now as well and have started to make up bearing blocks that mount instead of the steppers on the metal mounts. See pic.
So the lead screw goes through the bottom of that prototype black block, next radial bearing and on top of the outer ring rests the thrust bearing which again takes the load from the clamp on belt pulley. So I will have two on the forward side and one centered in the back. All three lead screws then joined by a loop belt plus one idler for tensioning.. I am not yet sure if a triangular belt drive has enough engagement on the teeth of they pulleys, if not I have to add a few idlers that wrap the belt around the pulleys more for better engagement of teeth. I intend to drive the rear single lead screw from a top mounted NEMA 23 or if that is not practical use a very short belt loop to drive the lead screw from a separate pulley and the motor in the base of the printer, not yet sure which I do. When I bought the pulleys I assumed its easy to get 3mm pitch belt but turns out that is not really the case, I have to make a mock up 1st now to see what length I need. Also forgot to order the NEMA 23 and motor mount (silly me).
Re piezo, guess that was kind of clear just I did not cop on to that, it needs a sharp impulse. Now with the glass bed it has never missed. Works very reliable now and wile bed levelling never probes on point more than 2 times, before it could take 4-6 times cause of the flexing nature of the flimsy light aluminium bed with the spring steel sheet. So for now I am all happy with the precision of the piezo. I will try again the other hotend mount with the build in Andromeda piezo.
Oh that sounds bad with the Mosquito, are you working in hot environment ? What you write re cooling issues would suggest issues will come up in an enclosed printer. I would not mind a 40 or 50mm fan as long as they can run silent. Or even a blower could them be a compacter, less noisy option. For an enclosed printer it may even make sense to have some sort of light weight duct with external fan to get cool air from outside the enclosure. Just thinking out loud, not there yet. The Linear Rail version will get the BMG M and Mosquito.
Have Fun.
Jan
PS: Re the termistor on top, that would not to control the heater but to delay the print start till the heat has gone through the materials. I find some way to implement that in the "Start G-code" section of the Slicer. IDK yet how I best implement that practically with a pocket cut in glass or whet ever, I probably have to experiment a bit.
My 2 NEMA 17 can drive Z WELL fast enough to trigger the z-probe. I just don't want to have huge inertia behind it with high speed if I can avoid it and go slower.