I am planning to have the countertop fabricators use some cut off pieces from doing the counter. The quotes I've gotten for the curb and niche are pretty cheap, since the material is basically garbage at that point anyway, it's just the cost of cutting it to size and grinding the edges.

The top of the bench is a different story, since it needs a bigger piece. it's minimal if I have to buy a full slab of quartz for the vanity. But I'm hoping to get a remnant, so there might not be enough left over. Buying a full slab so I can have the bench done in the same material is a lot more money. So I'm accepting that there's probably going to be grout lines there.

But there's going to be a lot more grout lines on the floor of the shower, so I'm not worried about it from a waterproofing perspective.

We have no bench, but otherwise we did exactly what you are proposing. We have quartzite for our counter, curb threshold, and knee wall. I really like how it pulls it all together, and how clean it looks.

We used leftover granite from our counters and tub decking to create the curb top and the shelves inside the shower niches. Most fabricators have scrap available so you don't have to buy a whole slab.

I'm with the others. While tile can be used, You're so much better off using the same solid surface as your vanity top (note I said solid surface and not granite or marble-- you CAN use siltstone, or any of the other man made surfaces). Not only does it mean greater longevity for the shower, but also easier to clean, and in the case of the pony wall and/or curb, makes for a better surface to install the glass onto. Makes for a nice design feature to draw thw whole bathroom together, too.

I definitely see the point about tying the whole bath together with the threshold, counter, knee wall top, curb, bench, and niche sill having the same material. I was hoping to do a Tere-stone countertop, but maybe granite or quartz for the rest except the top of the knee wall would have to be tiled so the granite/quartz didn't look too busy next to faux granite pattern on the Tere-stone. Tere-stone doesn't send anyone to template so I am paranoid about relying on my contractor to measure for these pieces plus I think Tere-stone would be more expensive than granite/quartz. My quote for a 36" vanity countertop with integrated backsplash, integrated sink, and 1 side splash is $625