At answering I put this into your quote and maybe not noticed:

Vertically yes but I have not thought to do square 5 and dia6 in 1 step, however it may work -you now as you go down with the mill you have the wider cross section down along the Z path so the 5x5 mm does not have affect to resonate-I think in alu should work especially on your machine

If you can - try this too -I am wonder if this works- perhaps this would be the fastest with chamfer on the wider edges instead of radiuses (1 step all what I can see in your dwgs)