Trim is specific to not only a brand but to the model as well.
Another thing to consider is that if you have all of those valves open at the same time, you will go thorugh LOTS of hot water, so you need to provide for that as well. You'll probably need a 3/4" main from the WH to the thermostatic valve - 1/2" to the showerheads would be fine. You could probably limit the number of valves if you could come up with a set of combinations and then use a multiport divertor valve instead of shutoffs. Quality trims can cost as much or more than a good valve.
If you haven't found it yet, check out www.johnbridge.com for help on tiling this new shower.