Looks OK in general and will work. Some comments:

Kress is noisy, have a look at the water cooled spindles with VFD drive, 1.5kW or 2.2kW. This will also have a better mounting surface than the Kress which is just held by a small collar area.

Make sure you have a way of adjusting the position of one of the X rail supports on the bed because you have trapped the X rails between the gantry sides, defining the position they need to be in. Easiest way would be to make the holes for one of the bed side profiles on the bed end plate slightly larger than the bolts.

Z axis rails and carriages can be swapped around to give more support. Put the rails on the Z plate and carriages on the Y.

20mm and 15mm plate will be OK. I've tended to use 6061 grade aluminium.