I am trying to create my first CBC project. I have drawn a horizontal clamp for face milling. Is this too ambitious? See the photos below. Any other suggestions are appreciated.

Looks fine, not sure what you mean by CBC but thinking it was a type and you meant CNC?

What I would do instead of maching the  locating bits  on the bottom part of the fixture would be to cut slots instead and inset keys into the slot. That way you have minimal material to remove where if you did it as in the pic there is a large surface area at full depth to remove.
Hood