I'm not a plumber.

Yes, you'll need to pick a brand and the valve but not the shower head or the stuff that appears on the wall.

For example, Moen produces a family of shower products that all use the same valve(s).

The rough-in would include the valve, but not the shower head or bar or cover plate or handles.

I suppose you could do it without the valve, leaving space where it would go. But it would be simpler if you already have it in place. And tell the guy installing it what is going on the wall in terms of tiling and such so he can get the depth correct.

Thanks weedmeister! So it sounds like I can mix products up to a point.

For example, if I love the look of a Moen thermostatic single lever trim kit, I would make sure all the stuff behind the wall comes from Moen and works with that shower faucet handle.

BUT, I could order my showerhead from anywhere? e.g. if I don't like the look of the matching Moen showerhead, I could get Grohe... right?

Actually, I'm pretty excited if this is the case, b/c I like certain showerheads, but not the handles that go with them, and other handheld showerheads, and yet other faucets.

Probably will be mixing Moen, Grohe, and California Faucets all in chrome in the same bathroom!