First, what is your local static water pressure?
The next thing to do is to determine how many outlets will likely ever be running at the same time, read their individual specs, and add up their flow. Then, look at the valve's specs to see how many GPM it can flow with the specified inlet. If everything aligns, it should work.
Keep in mind that this car wash will need a very SIGNIFICANT water heater. A waste water heat recovery system should likely be considered in the plan to minimize the size requirement. Those require a decent vertical DVW section to operate efficiently (i.e., they don't work well on a horizontal section).
You may need to upgrade your drain system, and consider multiple drains and larger diameter pipes. If you want to go with a steam shower, that is a whole other can of worms you need to add into the plans with its own requirements.
I'd also look into surface applied waterproofing systems. Pretty much all of the thinset manufacturers and some other specialty houses have their own, and you'll get various opinions on which one is best. If properly installed with good workmanship, they all work, and, IMHO, are superior to the traditional methods.