Of course prices vary depending on region & set up, but we too are down to studs and are building in a new shower. We went with a new shower head, hand held shower w/sliding bar & we're opting for a diverter with 1 valve. Cost to install by master plumber 380.00. He also is going to run the drain, which is an additional 150.00. The tiler is building the pan (or shower floor). I'm not sure what a trench drain is, ours will be centered. All in all you can plan for at least 600 - 800 in plumbing for what you're doing especially because you will have dual volume controls & the thermostatic valve, but trying to pin down costs through the forum is a wild card at best. You'd be better served by calling a couple of plumbing places to get a more accurate idea about what the costs in your area would run.

you'll have to most likely use a plastic insert to screw into unless you get lucky and hit a stud. In either case, just before you fasten the screws, fill the holes with Kerdi-fix, and wipe off any excess that squeezes out.

We have a Hansgrohe Aktiva hand shower/slide bar. Had to take out the water restrictor because it causes the hose to burst apart from the (whatever the technical name is) round wall connector. We went through five hoses before giving up and popping the restrictor out. No problems since. I don't like doing this because: 1) we're serious about saving water in CA; our drought is on its third year and this is the fourth serious drought I've lived through since moving here. So it's EXTREMELY wasteful. We take short showers and are putting in a gray water system. 2) I frankly consider the Waterpik in the other bathroom to be a better showerhead, saves water without the overpressure problem, and costs 1/10th the price. Our last one was still going strong after 17 yrs when we left in our last apartment. It is, however, not as pretty as the Hansgrohe.

Not all Slide bars with adjustable hand showers are grab bars. It has to say so and give the amount of weight it supports. Delta has both regular Slide bars with adjustable hand showers and adjustable slide bar/grab bars. You can buy it assembled or pick your own parts to pick the shower head you like. I liked a longer shower/grab bar and searched the Delta site for their longer grab bars and the separate hand shower mount and separate hose and elbow. https://www.deltafaucet.com/bathroom/product/51500 https://www.deltafaucet.com/bathroom/product/51600-SS https://www.deltafaucet.com/bathroom/product/51900-SS https://www.deltafaucet.com/bathroom/product/56302 Separate pieces to build your own https://www.deltafaucet.com/search-results?searchTerm=grab+bars https://www.deltafaucet.com/bathroom/product/U6500-RB Hand shower mount https://www.deltafaucet.com/parts-product-detail?modelNumber=U495D-SS60-PK -Hose https://www.deltafaucet.com/search-results?searchTerm=hand+shower+elbows