In a previous post I asked about using a transfer valve for three fixtures in shower ...wife finally decided she only wanted two (shower and a separate hand held) so we shifted from using a transfer valve to using separate volume valves, but local plumbing supply house is telling her she doesn't need 3/4" thermo valve and should use 1/2" - given this is second floor master bath on a well with pressure tank, I think we do, and worst case while more expensive by about $100 it doesn't seem like it could hurt. Thermo valve is Kohler 2975 and volume valves are K 2977.

I was gonna just T off the output side of the thermo valve and run to each fixture head. Should i just go straight up to a T and run left and right off that, or is it OK to run T "sideways" off line to shower then other fixture off that? i am assuming when one is open and you select the other volume valve there will be some momentary rebalancing since is a simple T design? Could I just use the tub outlet on the thermo valve instead?

Thanks!