Wow. Let me work through your questions. I am the one with the Transolid shower, by the way. I am not sure I have seen anyone else here with one.
Point 2: have you missed any manufacturers of solid surface pans? I don't know. I know that there are other solid surface makers, not sure if any more make pans. LG Hi-Macs is another maker I have seen mentioned just this week in the Bathrooms forum. Have a look, the person answering linked to a brochure.
Points 4 & 5: Yes,, you understand how a horizontal niche is made. Niches can be purchased along with your solid surface walls. You have to be willing to cut a hole in your wall panel to install it, though. That can be scary if you are not a pro. You caulk a niche in place, and since they have a lip all around, there is a nice place for the caulk to go that makes it hard or impossible to see and then it is waterproof and you do not have to worry. They come already having a sloped (and sometimes grooved) bottom for the water to drain out. Kohler makes a wall grab bar that is modern looking and is flat on the top to use to hold your stuff, too. Then there are the many baskets and corner shelves and corner baskets. I was looking at them for someone recently and was impressed at the variety now available. Look at Qualitybath.com or Build.com or the site of your choice and look at all that is available. You may decide to do a shelf instead of a niche. It CAN go on your outside wall. (BTW, I thought that a pony wall was a short wall, like next to a toilet, that does not go to the ceiling.) Some people put a niche above the shower valve and below the shower head. if you are going to put a towel bar in a shower, go ahead and just make it a grab bar. That is safer, since folks will grab it anyhow. Check Moen and Delta for lower cost ones. Jaclo is more expensive, but there are a lot of design choices and lengths.
Point 7: No, you do not need to waterproof under a solid surface shower pan because the only place they can leak is where the drain is. You embed the shower floor into a bed of mortar, usually, when you install it. The surface you are installing it on has to be flat. I do not know if anything needs to go between the mortar and the concrete. Mine was on a subfloor.
To best understand about installing the solid surface showers, go to one of the sites that sell them and look for a link to click to see the spec sheet and another to see the installation instructions. Really get into them and make sure you understand them. Any brand will do, so even look at a few brands. I fully get the needing to understand everything in order to hire the right person. I think you need someone who can build the stud wall to exact dimensions (plumb and square), cut the panels correctly and figure out just where to place the holes for plumbing that need to be cut, and who are willing to read and follow instructions. That last one can sometimes be hard to find. Not that they can't, but they won't.
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Veritek NO Swanstone or Transolid yes
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