The biggest issue you are going to have is with the extrusion the spindle is mounted to. When it's all the way down, it will have a lot of flex. May be OK for foam, but not much else. At a minimum, add some side panels, maybe 100mm deep and 10mm thick? Or a much bigger extrusion.
If it were me, I'd tuck all the motors out of the way by flipping them and using a belt to drive the screws.