Hey there - I was going to suggest the schluter edging as well - we used it on a floor, and a friend has it in her kitchen and while I'm not like "WOW! Awesome edging!" I basically don't notice it. It comes in an awesome copper color that blends perfectly into slate... but that's probably not helpful to you! Also comes in brass-like and brushed stainless-like. We used a mix of tile behind the stove and beadboard everywhere else, so wood was already in the mix. That being said, we used .5" x 1" sticks to frame out the subway. I hated it at the time, but now, again, don't really notice it. May not be for everyone, but here's a pic so you can see what I'm talking about - we did buy the bullnose pieces for where the tiles are next to the painted (orange) wall - but needed a transition between the beadboard and tile - bullnose wouldn't have worked well and the tiles and beadboard are different thicknesses, so they didn't make a smooth transition on their own.

Here's what our fabricator did: Before counter installation: this was an existing window and we didn't move it. The distance from the countertop to the bottom of the window opening would be less than an inch. Right after the counter and window sill were installed. Our fabricator laminated a piece of material of the thickness needed to the bottom of the sill - similar to what is done when making the counter edge. I think it would look right under each window as an extension of the sill and ending where the sill ends like ours does or under the whole group of windows. It may be easier to fabricate doing it the first way as it would be a very long thin piece for one piece to extend under all 5 windows. It looks like your filler will have to be thinner than your granite slabs so it may be difficult/expensive for the fabricator to make it extend much wider than the sill for the stacked appearance you want. Our fabricator did say that he was able to make thin pieces with our stone that can't be made with every stone when he made the thin pieces to trim our rangetop. He fabricated these pieces which are less than 1/2" high and ~3/4" wide (the slab thickness) and a bit over 2' long to fix a slight error they made when making the rangetop cut out. But I think the thin piece for the window sill wasn't as much of a concern for him because it was laminated onto the sill when it was made and didn't have to be carried around separately like the rangetop trim pieces.

No-casings and painted sheetrock returns are the right look for a modern house, and the major brands of windows have all gotten on board with all-fiberglass or for Andersen, all fibrex, windows, this class of windows having relatively shallow frame depth, and all offer dark colors same outside as in, to achieve this popular new look in "modern." The #1 favorite color is black, followed by dark bronze. To do it right, the carpenter needs to properly shim the opening before the rockers get there, so reveals are consistent all around. Insider Carpentry channel on YouTube has a great vid on how to do this right. The rockers need to mask well, then use a tearaway bead at the window side, and a good corner bead at the outboard sides. The best look, IMHO, is to have a 3/4" thick sill at bottom with the same window reveal as the sides, so the bottom of the opening is not shimmed in as much as the sides. To get this right, the window sits up on shims at installation time and the bottom of the opening is only shimmed to get it dead level and flat for the drywall corner bead. That sill gets no apron under and has to have a good plate-like bed. Anything more than 3/4" looks to beefy. Sills should have tiny returns. Here is a 3D render done in Chief Architect of a window with sill and another without. The windows are modeled at the same dimesions as the all-fibrex Andersen Series 100, the wall is 2x6 framing, and the depth of the returns to the drywall face is 4-9/16". Note the very shallow bullnose on the sill edge, and the small return. A painted wood or stone, metal, or composite sill is going to be more durable and easier to wipe clean than painted drywall, no matter the paint. And as for the dust on those vertical returns at jambs, or horizontal across the head, and durability, you have all kinds of drywall corners eleswhere in the house. Why are corners at windows going to behave differently. If your builder has not done these no-casings openings before, think twice before asking him to do it. If he has, insist on seeing examples of work. You don't need to be a first time event for the builder, his carpenter, or his sheetrocker.

Yeah, I saw what looks like Hydroban or something like that in the subsequent pictures, but nonetheless nails below the curb are a no-no.... The pan liner is the primary waterproofing membrane and that is compromised with a nail puncture. You can't rely on the secondary waterproofing layer 'hydroban' or what ever it is 100% to prevent leaking through to the cement board in my opinion. In the other pictures, it didn't seem like all the seams were taped and mudded with thinset before application of the liquid. Also besides that, a liquid membrane has to be applied according the manufacturers instructions, including a spec for thickness of the membrane. Painting on one coat is usually not enough. I think the next company you have coming in will verify this and you should get as many opinions as you can. Was the pan ever flood tested before the tile was set? If not maybe your next guys could do that. Basically you insert a plug into the shower drain, fill it up with water, leave it for 24hrs or longer... if the water level doesn't change, and you don't observe water leaking into walls you might be OK. But in my opinion the pan wasn't done correctly.