Planning a shop build, any suggestions?

With the plumbing in the concrete, a vapor barrier and 2" solid foam insulation you will have 6x6 metal wire mesh that the PEX heating pipe will attach to the top of the wire mesh. Make sure to cut every other mesh at the locations where you are cutting your relief cuts. Fill the cuts with poly and then absolutely paint or urethane the floor before anything is moved in.
I have painted pontiac symbols and mopar symbols on floors before.
Here's the thing. Once your pluming is in the concrete it becomes very difficult to locate those pipes if you need to drill anything into the concrete. Specifically your lift or lifts.
I tend to make the slab 8-10" thick at the locations of the lift pedestals. Make sure your plumber does not install any heating pipes into the thick area of the floor. If you plan on other, different lifts in the future, I tend to make a strip along both sides of where your main lift work area will be that run the length of your vehicle with several extra feet. This way in the future you can drill into this extra thick concrete and not worry about hitting pipes.
A pit can be a good idea also. Easy to cover with a metal strip when not in use.

Are you planning on using an on demand heating system for the floor?

I build several garages a year that are additions to the custom homes I build.