Hi Tony, I'll watch you build this machine with great interest having gone through similar planning stages when building my surface & cylindrical grinder.
I note you haven't mentioned grinding dust protection for the rails and ball screws. Are you relying on the built in dust seals of the linear bearings as its only occasional light duty use? Dressing the grinding wheel will cover all those precision parts.
Have you considered using coolant when grinding and drainage of same?
The vertical control movement should be as fine as possible for grinding. I used a motor for rapid up down, then switched to hand feed to the ground surface with a very fine adjustment. There will be some conflict of priority between the mill/shaper and surface grinding feed needs.
Lovely challenge!