Personal opinion...Kohler stuff looks and is generally built well, but they have been in the NIH syndrom forever...they like to do it their way, ignore history of what has worked well, and are changing designs constantly, so it can be very tough to find parts....yes, everything eventually needs parts. Plus, their stuff is designed by a engineers that may never have installed anything in the real world. Some of their stuff has all of about 1/16" tolerance - try getting that just right with a tiled wall!
A steam shower is a much more complex thing than a conventional shower. Make sure either you, or your installer knows the 'rules' and follows them exactly.
Benches require quite specific construction details so that they don't leak.
There are quite a few approved, tested ways to build one, and many more ways to mess up!
A handheld on a shower bar can be quite handy if the people using the shower are of various heights. I'm fairly tall, like the head high enough so I don't have to duck, but that might tend to be too high for 'normal' people to adjust. A bar helps in that manner. The handheld is nice because you can point it anywhere you want!