How many shower heads ? how many body sprays? What are their flow rates?
How many do you plan to run at the same time? What is the flow rate of your Thermostatic valve? Do you need or want more than one Thermostatic valve? How many volume controls or diverters do you need? How many shower heads or body sprays will be on each volume control or diverter port? What is the flow rate of your volume controls and or diverters? How many minutes will a person be in this shower typically and how many people will use it in succession? You have a 1" line to your shower already or is that the size feeding your entire house? Can you get a 1" or 3/4" line to your shower if it isn't there yet?
EDIT: miss read your post , must of been awake too late.
Need to know your gpm of this super shower system before you can size your
water tank, line, heater, pump system, ....