I'm a novice (not an expert) but I'll share what I learned in my recent DIY tiling escapade, which was also in my bathroom. I have caulked a lot all over the house, inside/outside, and I never worry about exactly how large a hole I cut on the tip off the caulk. I just make sure it's large enough to easily fill the gap, and go back and smooth it with a wet finger. On my bathroom tile, the corners weren't exact either, some tiles were a tiny bit closer than others, so I had the same problem with different sized gaps in the corners. No fear, just caulk it with a color than matches your grout, it'll disappear and blend in. I was really surprised how easily the caulk came off the tiles, after it was dry. So really; I found it was easier than I thought: just make sure the gaps get filled, wipe it smooth so it looks pretty in the corner, and the excess comes off easy, after you let it cure. What I'm trying say is that it's easier than you think it'd be. My bathroom has baseboard trim, so I didn't have to caulk that edge in a visible way, it's covered up by trim. But I'd guess the same rules apply.

I don't like the look of tub/shower surrounds, so said "thanks-but no thanks" when our contractor friend suggested using one for our guest bathroom shower. We also tiled the tub surrounds in our hall bathroom and MB. DH used hardibacker (cement board) for the walls, and then rolled/brushed on Laticrete waterproofing membrane. He made sure the boards were well-coated. Our tile guy used thinset to set the tile (Do NOT use mastic). We used regular TEC grout in the guest bathroom, TEC XT in the other two. We sealed all (grout, stone, border tile) after installation. We spray the walls with a daily shower cleaner/spray after each use (switched from Clean Shower to Mrs. Meyers Shower Cleaner because the clean shower is not stone-safe). We also wipe the tiles (and caulk at the base of the walls) with a piece of paper towel after showering (could also use a squeegee, just haven't found a squeegee I like as well as the one we have in the guest bathroom)--probably not necessary to do this, but it keeps our large format tile(s) looking nice (and streak-free), and prevents water puddles along the tub edge/rim from sitting for long.

Kitchens are one of the places you can get away with mastic to attach tile. You are not going to get enough water on a back-splash to make it through the grout joints unless you are flooding the kitchen. The grout joints are the 'weak spot' for water penetration. Repeated wetting (like a shower enclosure or tub surround) can allow enough water through the grout to start problems. Even in a wet location, an additional barrier is used to prevent water from moving through the grout, the thin-set, the backer board, and into the studs. You need to be very clear that 'waterproof' often means water does not damage the material, NOT that it stops water fro passing through. While cement board is 'waterproof' is is a cement product and wicks water (like grout) very nicely.

Wow those pictures look so nice.... I knew I didn't like visible caulk running along every tiled surface that met the wall. :-/ Quarter round was used in the models that had wood-type flooring, but like I said, the tiled floors all had goopy messy glossy caulk. :-( Is it at least paintable? The house we're looking at now isn't custom, it's a tract home. Options are limited, but I was asking more for reasons of proper alignment of expectations. ;-)