Here's my criticism from 30+ yrs in the kitchen/bath biz. (constructive, I hope - but YMMV)
If you want to run two heads at once, you're gonna need a hefty supply line and a lot of hot water. Large tank or high cap. tankless.
I'd suggest a smaller head on the handshower. It will look less cluttered and do you really need two rainshower sized heads ? ? ? If you want to use that handshwr bar as a grab bar , you better put solid blocking in the wall behind the mounting points , cement board and tile will not be sturdy enough.
You're lighting plan is iffy. As shown , it'll create shadows on top of your head while standing at the vanity. The pools of light in the tub end will be not be pleasing either.
You've also mentioned current location of ceiling fan and floor vents won't need to be changed. While providing a cost savings, if your fan isn't over or in real close prox. to the tub - it isn't going to do it's job. I'll also wager what you have is woefully undersized for the space AND its duct work is poor - adding to the poor performance.
Timers are great for fans because even properly ; they need to run for a bit of time after your bathing finishes in order to exhaust the humidity. They are waaaaaaaaay more reliable than built in humidity sensors embedded in bath fans. Only drawback is you gotta train your brood to use them.
The recessed medicine cabinet with integrated LEDs look cool, but I'm thinking it might be a fad?
And you're worried about this why ?
Is it more or less trendy than subway tile ?
Be aware that many only provide supplemental light and aren't bright enough for primary lighting - especially the cheap ones.
I'd strongly suggest making you're niches larger / more numerous. Especially if you're bathing the kiddos. Also consider lowering one for when you use the tub. You're already thinking about the tub control height, but forgot about the bath soaps, candles, loofas, razors, ect....... ?
Re: wall mounted toilets - There's no free lunch ! You've still got to have space / sq. footage for the tank. While they are marginally less deep than a standard toilet, they still require 4" and preferably 6" of wall to conceal the tank. You're just transfering that footprint from one place to another. If that wall is an outside wall .......
fuhgeddaboudit
All wear parts are replaceable without removing the wall covering.
If you're DIYing this I will also recommend a different approach than Kerdi. I'm a big fan of Kerdi and have it in several of my personal baths. But it has a steeper learning curve than other products/ systems. I would suggest using liquid applied waterproofing like Hydroban or KBRS showerseal -or- Aquadefense which is the same stuff. Just not Redguard. I'd paint that over GoBoard which is foam based like Kerdiboard. Kerdiboard would be easier too, though not as fast and a bit more expensive. Wedi is also good but even more expensive than that.
Bottom line is Kerdi membrane is a bit overkill for a tub/shower alcove. Moreover , it is a bit finicky for the first timer to properly mix the thinset to the right consistency, trowel it on fast enough and add the sheet before it starts to flash off, and smooth out the sheets. Then there's the inevitable corner buildup that happens no matter how good and experienced you are - which creates issues to deal with when you go to lay tile. It's exacerbated when using small tile.
None of this is impossible, but it's time consuming and frustrating for the neophyte. Using a caulk gun and putty knife to smooth sealant in screw holes , then painting/ rolling on thick paint and imbedding thin 5-6" fabric that folds easily and keeps a crease into corners is well within most people's wheelhouse even with no prior experience.
If your vents are in the floor, you may like these:
https://www.contractorsdirect.com/chameleon-vent-registers
- or -
https://ariavent.com/