If you want a clean/sleek finish using only the 12x12 mosaic sheets, like this image here, you will need to have a glass cutter to cut the edge that goes against the cabinetry.

remove the window sill (don't worry, it's not structural) and tile the wall and sill.

I don't get the whole backsplash thing. You're buying expensive tile and putting it higher than any "splash" is likely to occur. It seems like a fad, like fake restaurant stoves. A 6" high backsplash is sufficient to protect your wall, then you could have a narrow shelf under the cabinets for small items.