I have the Subway Ceramics Avalon / Minas with a medium gray grout. And a Shaw's white sink, if anyone is considering that, by the way. (My contractor could have ordered it directly, but at his request, I went through a tile store, and by the time everyone had put their sugar onto it, it was OBSCENELY expensive.) I'm not an installation expert, but at least with the Subway Ceramics, the installers use little plastic spacers between the tiles (I think some others have their own spacers?) when they put them up, they don't do it freehand, so how much grout you get is a function of 1) the limits set by the curvature of the tile and 2) what size spacers they use. So you might be willing to go a little darker with a smaller grout line, or with a handmade tile that refuses to go close together, you might want to stay light. The traditional color is close to concrete. But most modern people don't seem to like that, so do what pleases you!

Mikebeth - it took us forever to choose the tiles, mainly because we were undecided on the material at first. We thought we'd go glass, then decided to do a handmade ceramic tile in a matte finish. They are white with a grey undertone, no crackle, just matte. Your kitchen is great. I personally think your kitchen would go well with a glossy subway tile, a white with a slightly creamy tone (as I believe your cabinets have a creamy tone to them?), and I think a bezel edge would look awesome (check out minidmoo's kitchen). Or you could do crackle. A subway tile with texture, I believe, would go so well in your kitchen. I wanted something more subdued which is why we did a matte tile. Our granite has a lot of depth to it. Here's a better photo of the tiles:

I can't answer all your questions, but most subway tile comes self spacing, so you probably won't need spacers. You may find that since homes are rarely perfectly plumb, that you may have to slightly nudge some tiles a bit this way or that to avoid a gap under the cabinets or near the ceiling. For example, without nudging an area of tiles up a bit in one area of my backsplash, I would have had a half inch gap between tile and cabinet - too big to caulk and too small to tile. By moving several courses of tile about 1/32 to 1/16 up, the gap became small enough to caulk, and the small adjustments were not noticeable. So measure each area before starting to see where adjustments need to be made. While you will not need spacers for the tile, you will need some to hold up the first course - you need a gap between first course and the countertop which will be caulked. I have done some tiling and did my backsplash. I used a small amount of pencil trim on one edge and it is difficult to work with. Consider keeping the wood trim around your window - it will save you a lot of headaches. If you use the pencil trim, I am not sure you can adequately cove the rough edge where the window meets the drywall, though you may have some smaller trim work in mind.

Many glass manufacturers do not allow the use of epoxy grout with their product. You must contact the manufacturer for this information. If there are no instructions in the box also inquire as to which setting material is called for. Some glass may require mastic instead of mortar. While you have them on the line ask about thermal shock rating. You have a large format glass tile (9 square inches is large format for glass) If you have a cook top, especially gas simply boiling a pot of water on the back burner could crack the glass tiles due to thermal expansion. Just a few things the DIY shows and box stores won't mention. Was any of this mentioned to you at your point of purchase? Always test grout first to verify it will not scratch the glass. Other grout manufacturers such as Ardex, Bostik, Tec should be considered also. Some make grout specifically for glass. I do not recommend glass tile installation for a DIY'er. or a GC/ remodeler. There is a lot more to it that I did not mention. Proper cutting, setting, polishing etc. If you think hiring a professional is expensive wait until you see the cost of hiring a amateur. Good luck with your project.