Do a practice run with all the jets, shower heads, etc. I followed all pipe, flow rate, psi etc and ended up with body sprays that tinkle and not spray when the 10" rain head is operating. On the 3 way valve only one port is larger and the other two are smaller .. I wished I had pre tested before the tiling.

If you want to utilize multiple functions at the same time, and have good performance, you'll need a separate control for each. The rain shower head uses all the output potential from the shower valve. I have one. I have 2 separate Hansgrohe control valves: one for the rainshower, the other for the regular shower. We can use both together and the water flow is just fine. It is important to run 3/4" lines for the hot supply right up to the where the branch tee's off to 1/2" for each shower control. 1/2" lines can really only supply a single shower valve at a time.

The inputs and outputs for a shower control valve are all 1/2", therefore they are not sized properly to supply 2 fixtures (i.e. rain shower and body spray) at the same time. Use separate controls and you will get the best performance.