Pretty much every master bath I've designed and built over the past umpteen years has had two heads. Some have had more, but I try to keep it at a max of two heads. Think basic bathing needs. For that you at least need a "standard" shower head, with a standard type of spray to wash and rinse hair. Then think shower experience. Some folk like the multi-spray heads. And that's fine, that can be combined with the "standard" head in the previous paragraph. Some like a rain shower head. A true rain head (a gentle shower of water droplets) can give the best "rain experience" by being ceiling mounted and away from the wall. Rain heads should have the water dropping straight down. So mounting it on a somewhat short arm coming out of the wall may not do the head or the bather justice. Think practicality of cleaning up the space of a larger shower. For that, a handheld on a long hose is a great addition that allows you to easily wash down the spaces in a larger shower. Then there is always the plumbing cost and the cost of the additional fixtures. There are affordable valves that have a built-in diverter. Or you can plumb in two supply valves, one for the "standard" head, and another for the rain head. My somewhat standard setup these days is the "standard" head being a handheld on a hose. The handheld can be mounted on a sliding bracket for adjusting the shower head height; higher for a tall bather, lower for a short bather, or even lower for shower from the chest down. Most handhelds have accessory wall brackets. Example, you can add an extra bracket to hold the head at thigh-height for shaving legs. The length of the hose on the handheld can allow you to use the handheld to rinse down the far-flung corners of the shower. Or to wash pets. Or young kids. Personally, when using the shower head and the rain head at the same time, I prefer the water to come out of the rainhead at a different temperature. So instead of using a single supply valve and a diverter to supply both heads, in my own shower I have two separate supply valves; one for the handheld and one for the rain head. The cost of the two valves combined was less than one of the fancier supply valves with a built-in diverter. Having the spray from the overhead rain head offset from the wall-mounted handheld can allow two bathers to shower at the same time. So there are various ways to skin this cat. But in general, for a larger shower that will have a single head, I do recommend that the single head be a handheld on a hose. If users want a "shower experience", then I'd recommend adding a second head and that the second head be a true ceiling mounted rain head. If there is a third head, that head can be a fixed location shower head on a standard shower arm coming out of the wall. Just my opinion. When you go to more than three spray heads, then you have to increase the size of the shower's drain and drain branch lines to remain code compliant.

I can't help with the wall outlet and holder, but I have a similar Hansgrohe hand shower (not the exact same model, but a raindance type) and hose - I've been using them for about a year now and I'm super happy with them!

Anyone know of an additional part I can put on my brand new watermark showerhead to limit the flow of water? The handle only lets me adjust hot/cold, not flow/pressure. I think there are like $4 parts for this, but need advice. Thanks!

You are making this much too complicated. A show-head is a shower-head is a shower-head. It has no moving parts, so it is unlikely to break. Pick one with those little nitrile or vinyl nipples so its simple to de-mineralize that matches the finish of your shower. Go to Build.com, search for shower heads, set the sort filter to "Price (low to high)" and pick the cheapest that meets your needs. Restoration Hardware? You're kidding. You must just like to spend money.