I think the first layout is fine. You might want to consider moving the door for the storage room of the master bedroom so that it opens into the hall. That way the kids can use it for overflow storage. Also, that hallway is big enough that I think it could hold a large armour, providing more closet space. (There's no need to sleep in the same room as your clothes, so long as they're not too far off.) Also, don't forget that while the drawing shows kids in double beds, this need not be the case, so there will be more room for furniture (dressers or whatever) in their rooms. Finally, that step to bedroom 4 will not be odd at all. I've seen it in other homes. It looks clumsy in the drawing but it isn't. What you'll see when you come up the stairs is a bedroom door on a slight diagonal. It's only an odd jagged step if you walk like a robot, in straight lines along the wall, which is what your eye is doing on the drawing but you won't do in real life.

Same wood as the wall, with triple coat of varnish to prevent problems. Around the faucet, a solid piece of material, perhaps a solid porcelain tile drilled for the taps. Keep it very simple.

An all weather outdoor shower is easily done by locating the mixing valve inside the house and use a coupling shaft to locate the handle on the outside. You must use a standard tub type lower faucet (with the pull up to activate the shower) to allow the system to drain out when the shower is done. You also have to make sure everything slopes in direction of the water flow. We live in Bancroft Ontario so winters are well below freezing and we have been showering outside for 3 winters. Only issue we have is the shower head will freeze so we typically remove it after a shower or shower without it on when really cold. The system has worked well and it helps that nothing special needs to be done by anyone. no inside valves to close etc. Just turn off tap and everything drains.

Normally a hot tub comes with a means of heating the water, and maintaining it without having to empty the water. This is where water filtration and disinfection methods are worth it and less wasteful. It really doesn't matter whether it is stainless steel or not: you are heating up water to levels that naturally promote bacteria and algae. Hence the NEED for some type of disinfection - which can range from tossing in a chlorine table to add ozone or other types. I suggest you purchase a book entitled "What colour is Your Swimming Pool" 2003 edition. It will give you a practical guide to what you are looking for to maintain your spa tub and why you need to do it.