Agnes, you want a carpenter or contractor or handyman who knows how to scribe to make the surfaces fit together. No wall is square. The sheets of material ARE square, so to fit in your space, they need to be trimmed to fit.
Some shower kits, like mine, divide the back wall horizontally or vertically. Others, like Swanstone, give you a one-piece back. You have to decide for yourself which look you prefer (or like me, if you will settle for the other look!). Trim pieces may be involved with the division of the back wall, or may not. Mine did not use trim at that point. My trim pieces that you see going around the shower are at the point where the regular wall height ended and the extension kit started. There is also the nice squared off trim around the outer edge. Then there is a cove trim on all of the inside corners. Other shower wall sets may have cove trim on the inside corners, or may simply butt them. I am not aware if any will sell you the extra cove set so you can trim out the corners between the ceiling and the walls, like Transolid did. (They just kept sending me trim pieces until we got the right ones. I think they realized they goofed by not having figured out which ones to send me in the first place.)
I love my linear drain, but I back it up by having a drain in my floor. If my linear drain should fail, or any of the bathroom plumbing leaks
or overflows, I have a drain in the floor in front of the leg of the
vanity that will catch it. That means that the floor of the room is slightly sloped because it is essentially an entire second shower system! My contractor bought a Kerdi shower floor system that sloped the floor to the drain (it was super-hard foam), and covered it with Kerdi membrane that went up the wall 5". The room's entry area was outside this "shower" area, and has a Kerdi foam ramp underneath that gives it a slight slope up from the room threshold to the "shower" area. This also keeps the water in the room's "shower" area if a major flood occurs, and away from the room's door. So far, there is no need for the second drain, but I could imagine a washcloth covering the main drain, or over-spray if a shower user did not have the curtain closed right, causing water to go out onto the floor. I also have three shower heads in the shower. I use no more than 1 1/2 at a time, which the drain can handle. If someone turned on all three, water could escape the shower. They would run out of hot water pretty quickly, so it would have to be a short shower!
These are the kinds of considerations you have to take into account when you have a level-access shower with a trench drain that slopes to the front of the shower. I would not do it without the room drain, and I believe that it is code to have the room drain. I just like having the room drain in general, too. They are standard practice in other parts of the world and I don't know why we never did them in the US.
As for your feature wall in Cambria, it could be very attractive if the stone were used in the countertops, too. You would have to choose the stone and the solid surface very carefully to get the right look. I imagine you could butt the SS to the Cambria and caulk the joint, but you would have to talk to both the Cambria and the manufacturer of the SS to be sure. Are you sure that you don't like any of the Choreograph choices? They have a very zen feel in their sedimentary rock look. (Though I understand that you have to order way ahead of time due to slow delivery.)
One thing I don't like about my Transolid product is that the color/pattern differences in each panel are obvious and bother me. The amount of veining and gray cloudiness over the white vary enough that one section of the shower looked really different to me compared to the rest. Adding the trim pieces to section off the panels really helped me to get past that, though. I was surprised that this worked, and is a good aspect of having the trim.
Q
Dark penny tile, dark grout
Q