If you have to go with a visible niche, here is what I did. I went to Bath and Body Works and bought several bottles of shower gel. The shower gels come in clear plastic squirt bottles with silver chrome-looking tops. I emptied a couple of shower gels into spare bottles, removed the labels, and put my other products in the empty BBW bottles. Then I marked them on the bottom with a sharpie to identify: B for body gel, F for face wash, S for shampoo, C for conditioner. You can’t see the sharpie marks. The bottles look really nice in the niche. BTW I have a custom niche that was sized to work seamlessly with the tile I chose. EDIT: I would consider doing the border on the bottom of the walls like a baseboard to make the shower floor look bigger. Re the niche: I was warned about water seepage as well, so I towel dry the niche after every shower. It’s not a big deal. Also, my custom niche was framed out inside the wall so I could put it where I wanted. (My shower is small: 30x 60) Also think about how much water will be hitting the niche. In the pic with the pony wall, there might be a lot of water coming at the niche. My niche sees hardly any water because the shower spray hits the floor several inches before it gets to the niche wall.

Thanks a lot for all valuable information. Actually I noticed one thing last night, when water is flowing thru the down spout, it makes more noise than when water flowing thru the shower head. @nancyinmich Oh yes, I did not even think about that. The reason I thought about the spray foam is, it could expand and fill in the gaps, and I just have a make a tiny hole to spray. But I believe, if I have to install insulation batts, I probably have to cut the drywall, right? The other side is hall, and the walls have texture, (which I don't like even a bit), so it would be hard to cover it all up. :( How about the loose fill insulation? I have watched videos about this. But I am afraid, the insulation may be fill in all the gaps, especially with the water valve. @Jake The other two bathrooms are very silent, both from the bathroom and the other side. Again, likely because of insulation. The bathroom that makes noise, the sound is loud both in side bathroom and other side too, which is hall/kitchen. And this bathroom is right in the middle of the house, so the sound is also audible from the living room. If you think there is some problem with the valve itself, how can I narrow it down? Does it leak water inside the wall? Shower works fine with good pressure like other bathrooms. I also wish I would not have to open the wall anytime soon. If not the spray insulation, what other insulation would you suggest? @ionized_gw That's a good place to start. @Bruce, Since I want to fill up the space between two studs, I was thinking of using the gaps and cracks. My idea is to , make two small holes, one below the valve, and one above the valve. First spray below then valve, and then spray above the valve. I don't plan to full up the entire space between the studs, but just give enough insulation around the valve to make it quite and sound proof. I am still trying to figure out if the valve is bad, or is it just insulation like my builder suggested. @Austin Air companie Thanks for your input. What's the best way to figure out if the noise is because of the water hammer? It doesn't happen in other bathrooms. Also, the noise is worse when water flows thru the down spout compared to water flowing thru the shower head. Could it be because if the valve?

More notes regarding setting drain depths... once the rough plumbing is run under floor, whether its a raised floor or slab, the maximum drain depth is set, as slope from the sewer tap to the drain has limits. The installation of the actual drain fitting is subject to those previously set limits. Its really important to PLAN AHEAD. Curbless showers are still getting introduced into the market. I have one in each of my current homes underway, but only in the master. Installed my first over a decade ago for wheelchair access. Costs more to do. Cannot always retrofit as it requires lowering the entire drain system under floor 4". Linear drains cost more to do. Etc. Anything that doesn't cost more would show up in production homes.

Thank you! The 1/2" looks great, so that makes me comfortable moving forward with that. Yes, reviewing the guidance for the shower glass, I noticed the same note on needing it to be flush along the edge that the glass will wrap, so need to figure that one out too--but we may try to use the 5" top there and hope that it is exactly flush and not a fraction of an inch too narrow. That wall is measuring at 4.5" right now and will only have tile on one side, so I *think* it will be just shy of 5" finished, since the tile is 1/4" thick.