Great looking shop idea, man. I wish I had the space and means to build me one (my .49 acre ain't gonna cut it).
As far as your shop becoming too small- you could always come off the back side, or east side, with a closed in area for parts storage or something. With just a lean-to roof.
I like the plan. The only thing I might alter is the door to the east bay. I'd just make it bigger- in case you wanna move larger parts from the "clean" bay to the other side of the shop, without opening the big roll up door.
Anyways- good luck!