I just did a shower very much like yours with Kerdi for a local prep school here a few weeks ago. There's no need to fir out the walls at all. Just kerdi right over the block. I'm showing this last pic only because it shows the Kerdi drain. I wanted to take progress pics of this as I went, because I KNEW this would come up, but I forgot to, so there's my proof it's a Kerdi shower!! :-)

We want to paint these walls the same color as the house (egshell, light beige) or at least something close to it Trojan Color Sealer. You can buy color samples. 8 oz. for $8 plus shipping. Mix your own color to 'match' your house, just keep track of ratios so you can duplicate up into larger quantity. The sealer is semi-transparent and you can 'cut' the colors with clear sealer too. They will custom mix the sealer if you have over 15,000 sq. ft. and they mix to any paint chip. They're currently doing a big project at Disney with a special, custom red. Sounds too fun, would love to see that. Your concrete is well aged at 12 years so you don't have to worry about PH. New concrete has a litany of prep procedures so you're kinda lucky there. But the walls do have to be bone dry in order to spray on the sealer and it's a bonus if the walls have a rough vs. very smooth texture. Mike Kornell is who you want to talk to at envirosafe. 1-866-874-8070. Here is a link that might be useful: Trojan Color Sealer

I would put one in cab 21. It will not be a prep sink per se because it is not handy to the fridge AND stove - it will be more of a bar sink for the fridge area. It will keep people from entering your work triangle for a glass of water, though. Not sure if you are open to further layout suggestions, but if so you may want to post a layout thread. I'm not one of the professionals here, but I can see some potential issues with this kitchen - your barrier island (which won't be helped by a prep/bar sink because you have to turn the corner no matter what) and your aisle widths seem tight. I can tell your home will be lovely (look at all those windows!) but make sure it will work for you.

Sorry it has taken me a while to get back here. That area gets full sun and faces the east mostly. No shade all day long on the concrete. The rock wall is on two sides and faces the lake. It has a pool and concrete deck on top. It is ugly, but this is the country. The stairs go from the boat dock to the front door. The front door IS technically in the back yard. The massive concrete wall is a porch/patio on the top. Oklahoma has clay soil usually. It is on a slope so drainage is good. The gutters drain through that large PVC pipe in the concrete. I can paint that for sure. We live in southeastern Oklahoma. Deer and rabbits are everywhere. The deer sleep in the grassy area closer to the road and they are always near my carport and cars. No fear in them, at all. I thought about azaleas or rhododendrons, but they would not hide the concrete in the winter. Plus, it gets full sun. I guess I shouldn't worry about the winter because not that many people are using a boat in winter. That is the only way they could see the front of my house. On the upper slope, I have low growing dwarf crape myrtles. The taller crape myrtles are called Pink Velour. On the lower wall, I don't want something that has to be trimmed all the time like a hedge. I thought about nandinas, but there is probably something better. It needs to be no higher than 2-3 ft tall. Some type of fountain grass might hide the wall, but I am not sure about using it. Picture of my front/back yard with the rock wall and pool. Stairs are where the lower sidewalk is.