Hi GH, All of that water demand will, most likely require a 3/4" water line, instead of the standard 1/2" water line, be piped to the shower to deliver additional volume and pressure. Without that, you will not have good performance from using multiple sprays, regardless of the valve type or diverter option. And yes, the volume is cut in half with shared functions from a diverter, but depending on the shower heads, may still be adequate. It's a balancing act, and will depend on your water pressure from the street. For a standard 1/2" diverter, to just switch between functions, the Delta R11000 rough-in body is reasonable and good quality. Then you choose the type of trim option and a 6 function cartridge. Otherwise, if 3/4" water line is at the shower, separate volume controls will allow all the functions to flow at full blast.

jridh...this is why spray foam has sheetrock between it and the living space. and yes, burning foam produces a gas as it burns. thus the need for fire rated sheetrock. OP putting the foam sheating on the exterior is the best investment for foam for walls. proper nailing pattern, seams taped and any holes sealed prior to cladding install. the foam sheating can go on top of housewrap, and if you chose foil/foam board and have brick cladding..you get a radiant barrier for exterior of walls with 3/4' air space between brick & foil. air sealing doesn't just happen. even with sheetrock & plywood sheating,,,air will find its way in through any small gap & hole. to air seal you have to caulk areas like sole plates to slabs & subfloors, seal wire & plumbing penetrations and any holes into the house from both attic and ambinet. however...if builder has limited time for foam in walls or conventional..it is doubtful that he will be on board with adding foam sheathing to extrior walls. when you add to depth of walls...window and door framing/finishing changes. this is why I didn't recommend this, for your situation. itrw...the builder isn't going to spend time to make this happen properly. the last thing you need is improperly flashed windows & doors due to last minute add on of foam sheathing. usually people who use sheathing on exterior of walls go into framing with this in mind..not an add on later. although ithis is the best use of $$ for added insulation & air sealing qualities. of walls. it iis in the planning stages that foam sheathing is discussed...not once walls are ready for insulation. as your doors & windows are in place & flashed...I don't think it will reasonably happen now. what people need to think about is...the sun hits one wall at a time. but it hits the roof all day...every day. this is a better place to put the foam. if you have hvac equipment..ductwork, in attic and holes in the sheetrock ceiling..recessed lights oversized cuts for supply vents & bath fans...it is difficult to get these areas sealed properly. great stuff in a can is oten used..but it doesn't seal as well as people think..nor does it last. other things like kneewalls in the attic..changes of ceiling heights are also problematic. while they are usually insulated..they are not air sealed and allow attic temps to enter the house. over the years we have used the same foil/foam sheating to air seal knee walls & upstairs walls shared with attics to stop the air movement & temp gain. it is a tough install, thus another reason that the foamed roofline is so popular. this install will cover all of the builder/trades errors, allowing easier & affordable utility costs & smaller sized hvac systems. this late in the game...stick with air sealing walls insulate conventionally & insist upon air tight drywall aproach through out the house. and easy way to get it done is for sheetrock installers to install as if no moldings were being used. this will make sure that sheetrock is taped & floated behind ceiling moldings. closing leakage from attic into the house that is otherwise hidden behind crown moldings. google air tight drywall approach (ada) to better understand why this is an important part of the performance of your walls. best of luck.

I'm not a plumber either, but I would think that the "supply" should enter the loop in the middle of the right hand vertical portion of the loop. I would think that it is similar to the design of the manifold system that I am building for my water distribution system. My reference picture is on line and the link is posted below. It is from the website of Two Masters Plumbing in Toronto Canada (didn't want to take credit for their work). Here is a link that might be useful:

Plumbing solder is tin and antimony or tin and silver and are non-toxic. Lead bearing solder (for plumbing) hasn't been used in at least 50 years. Flux is used to clean the tubing and fitting. The 'old' flux used zinc chloride - the flux looks like Vaseline, apply a very thin film to the tubing and fitting, cleans when the joint is heated. Now understand this kind of flux was used for probably 100 years to solder copper water pipe. Today, there are NSF approved fluxes that are zinc chloride free. No need to worry. Further, once you run some water through the pipe, the residual flux is washed away. I have always lived / worked where there is decent city water, no problems with copper. Could very well be that well water, improperly treated, would react with the copper pipes. Also consider, that if you have to use PEX, cause the water reacts with copper - maybe the water should be treated - because (untreated) it may be less than healthy for you!