We will be using pex tubing for domestic water supply under a slab.  Should we insulate both hot and cold water lines all the way from the manifold ? Is there a difference in the types of insulation available?  Should we consider running the pex in PVC pipe in case of a problem later ?  How easy is pex to pull through PVC pipe?   How do we support the pex tubing from where it exits the wall and to the fixture? For example a toilet ?  Is the "home run" concept the best, or use a larger size main like 3/4 "  and branch off with 1/2 " to fixtures?  

Those are all questions your plumber will handle.

Larger size for the main.

I like to circulate the hot water because we have water issues outweighing heat issues.

Personally I do not like running pipes were I can not get to it if something goes wrong.

Insulation, well that depends on your situation.