Yes, you can totally do this--make sure you use a starlight glass tile since the regular tile will look slightly green. Did you see the white glass tile that Kaidan is looking at?

http://www.delphiglass.com/soldering-supplies/flux-finishing-chemicals/mirror-edge-sealant Here is a product, but there are automotive products that do the same thing. Its just a spray, and you could just hit the silver ones. Do you know what type of adhesive your tile person used? In mosaic we use thinset mortar. DRY. not premixed. Premixed thinsets are mastic based, and they WILL fail. especially outdoors. Your environment also matters. If you live in a dryer frost free area, it could be find for a number of years. The reason I ask is because mirror uses a special mirror mastic. I would never use mastic for anything I want to endure However, tile people often have different opinions about that. And I know when mastic is used in my region out of doors because I often pick up the broken tiles that have fallen off to use in my work :) I have obtained some very expensive ceramic that way. At any rate, here is an article for you. Good luck! http://tiletools.com/mastic-vs-thinset-which-should-i-use/

In general, the 3x6 staggered subway look may be a bit old, but I think that your two choices, 3x12 and 6x12, are both up-to-date and less common. Larger tiles have a more distinctive look and provide a clean, modern aesthetic. I think the stacked look or the brick pattern would both look great. In general the large size plus the stacked look will give you a great contemporary feel. You can check out the glass tile oasis website for some cool layout ideas. That’s where I ordered my glass bathroom backsplash tile and achieved that modern look by stacking them (It was the Sea Glass Tile Series). If you hate cleaning your bathroom, use larger slabs, since they making cleaning much easier. Smaller tiles also create an optical illusion and make the room seem much larger. In your case, where you are using it for the backsplash only, I wouldn’t say that one size is more associated with bathroom décor over the other. Hope this helps!

Did they just leave exposed cut tile at the end of the run? They should have used a bullnose tile, a trim piece, or Schluter. They should also have stopped the tile in line with the upper/lower cabinets and not with the counter. If you really don't like it, I would just plan to replace it a few months down the road when you have moved in and had time to relax a bit. Go to a good tile store with a lot more choices than a builder's design center and hire your own tile installer, with more skill and pride than the builder's crew. Many people don't install their backsplash till a few months after they have moved in.