That's an awesome idea. Lots of color, texture, robust surface for grime, etc. I'd glue 'em down using a siliconized latex adhesive caulk. (Siliconized latex caulk has more adhesion than plain latex caulk, but is much more removable later than pure silicon caulk. An example is a product called White Lightning 3006) Run a generous bead on the inside half inch edge and a zig zag down the middle then press firmly against the wall, checking that they don't shift. This will hold them fine but is also removable later with care. Just make sure the back sides are clean, for the adhesion.

Thanks again all for the replies. Things did not work out as planned, but maybe it's for the better. The helper showed up late, so I tried to look at the task myself. Decided to cut the caulking out between the wall and the countertop behind the cooktop. It allowed me to insert the backsplash downward enough for me to muscle the entire backsplash in place from under the hood. I preemptively shaved some drywall off where the gap is smaller than the thickness. Glad that I did because although I did it with the intention of trying out/dry fitting, I ended up having a hell of a time to back it out. Actually, it was so hard that I gave up. So, I simply brought the top forward to give me enough room to squeeze some adhesive in. Due to the awkward access, I just did snake pattern. BTW, the bottom two screw holes are behind the countertop and not accessible. The top two screw holes are so close to the hood and cabinets that I simply cannot go straight in. And when I tried, they were not hitting studs anyway, and I can't get the drywall anchor in. So, I'm mostly relying on the adhesive now to hold the backsplash. That's it. No removal in the future! When the helper finally arrived, he was surprised to see that I already finished installing the backsplash.

"I don't know how much variance there normally is on the sink install- should it be completely flush all around, or are there slight imperfections? There's really just one corner that is completely flush, the rest is "mostly" flush. Should I press to have this fixed, I don't know if it's possibly to fix it with the sink installed? I just did an oval undermount vanity cutout by hand and I'm sure there are "slight" imperfections. If the hole was cut with a CNC machine, there will be none, but the reveal is up to the homeowner discretion. The sink can be reinstalled by abandoning the fixed mechanical fasteners they've probably used and installing it with a Hercules Universal Sink Harness (Braxton Bragg). "Same with the side- do you normally custom- cut the granite to your space or just leave slight variances and cover it with caulk?" The reveal should be the same all the way around. There should be no "covering it with caulk". "Are all the bullnoses made in the same way- will I have the same problem with the granite sticking out too far with a different piece of granite, or did I just get a remnant that doesn't work well with my space?" No, you got an idiot templater. You could have them rip off the right end, but that may knock your sink off center. They could rip off the overhanging left end, reprofile and polish the edge which would not affect the sink center. "Should the granite have been sealed again, I don't think they did any kind of sealer at installation." Insist they bring a quality sealer and seal it in front of you. It will take a minute and a half and .50 worth of sealer. "I'm not wanting to be a difficult customer, not sure if I should insist on starting over or just live with it." You aren't being difficult. I would die of embarrassment if someone posted a picture of my job overhanging a wall like that. Have they no pride?

Epoxy a piece of 1/8" thick aluminum onto the back and bend away. I stood on a 4' long 4" wide piece of granite on 4" blocks at a trade show once. The stone went to the floor and didn't break.