Yes, that's a nice looking design. Your electronics box looks first rate and would be instructive for other people designing their controls. It's taken me 3 attempts and it's still not as neat and orderly as yours.

I'm curious if the base will be machined out of another large block of AL, or made of several smaller pieces bolted together. I've been contemplating using large blocks of solid stock, or perhaps granite/epoxy filled 8020 extrusions (to save on milling costs and allow me to do more of the machining).

I like the fact that the Y stepper is hidden away in the base, but will you have to disassemble the mill to get access? Perhaps an access panel on the back (or bottom) would be helpful. Also, if you ever want to convert to brushed servos, they tend to be quite a bit longer with the encoder - and might not fit in that space. AC servos or brushless might do the trick.

Again, these are hypothetical. If you will always stick with steppers, it's probably a non-issue. Looking forward to some build photos. It might inspire me to start on my own mill.

Steve