i would run 3/4 to everything..
to the shower head reduce right at it

use a 3/4 copper x 1/2 mip dropeared 90 for the head
even thou..the head has a water saver.

You should just reduce the 3/4" at each fixture.

That said, you will potentially have trouble getting the water volume that you want for two fixtures at the same time (4.5 - 5 gpm)from the 1/2" feed.

In addition, you need to consider your hot water heater (see the post about the 75 gal water heater not providing enough hot water).

I am going to tell you what I tell everyone in this situation...

1.) Multiple shower heads are a fad, but they are extremely wasteful of both water and energy. Both of these things are in short supply in this country.

2.) If you expect them to work, the system has to be designed for them including having adequate supply (not 1/2") adequate water heater (they will drain a 40 gal water heater in about 10 minutes) and an adequate drain to remove the water.

Thanks so much for the replies - I figured that was probably the way it should work, but I wanted to make darn sure.

Also, I did a ton of research and I am aware of (but thanks for the cautions!):

*adequate psi
*adequate hot water
*adequate drainage

This is one of the reasons I went with the Hansgrohe diverter, which restricts usage to only 2 functions at one time. (I could have used the Danze diverter which can run all 3 at the same time, or gone with volume controls for each function.)

I also went with the 1gpm body sprays for that reason as well. Hansgrohe even makes one that has a 0.8gpm mode, but it stuck out from the wall too far for our purpose.

Also, inadequate hot water can be solved with $$$ - replacing with a tankless heater is one option. And I've even seen add-on pumps to up PSI :) But the drain is a killer for sure.

Anyway hope all my calculations are correct. If not, we'll just run one function at a time & call it good. I am looking forward to those massaging body sprays after a long hike :)

Thanks again for the input both of you!