Having now seen it fit so well on the mill I think you would be better for off building a VMC, but optimised for wood, 400mm z axis on linear rails bolted to a column would be be no problem. The other way to deal with the large Z axis you need is to fit a 4th axis and then rotate the blade to the tool, I've seen furniture machinces work like this.

Are you going to be making a lot of these blades? if not it seems like you are building the machine to make a part but limiting other useage (hope that makes sense)

nice work so far, is that your workshop?