Your Z height is the largest I have seen so far on a MPCNC. Since most people are building these as cnc routers the z height only needs to adjust by a few inches. But it looks like you are after a very high volume 3d printer. You will probably have to reduce your z height by a lot to get really good results. Hopefully Vicious chimes in on this and can guide you in the right direction to get the most volume with a good print quality.