What about just having the Calcutta as the backsplash? Just run it to the bottom of the hood. No other stone or anything else needed.

I don't understand this question/photo. Are you going to rip out those old cabinets for new white ones? Are you going to remove the backsplash? If you want to keep the backsplash, new white cabinets would match. If you want a new backsplash, use a larger format style that includes the color of those old cabinets and doesn't compete with them. I personally would update both. The cabinets have seen their day, and that kind of backsplash is already dated. At the very least, I would have the cabinets painted a bright white and replace the countertop...although without seeing the floor, who knows?

I have a small kitchen too and I am looking for a 3" by 12" tile, but I am open to whatever works best. I like the brick-like proportions of longer tiles. But honestly, any tile is a vast improvement over the fake travertine 6" by 6" tiles installed on point (diagonally) that are on the backsplash now.

I think where to end the BS is more nuanced than to follow the simple rule to end it like you would a 4" BS. The 4" BS never tied in directly with the upper cabinet, so for that reason it totally made sense to end it at the end of the countertop. However, when a BS ties in with the upper cabinet, then it's a different situation. When you install a full BS beyond the upper cabinet, my eyes go directly to the "bent-elbow" or "appendage" sticking out to the side of the cabinet rather than to where the countertop/BS meet, which is lower than eye-level and is on a different plane. However, if the countertop and the BS are the same material, then yes, I agree that the BS should end at the countertop, but I still think it looks off to me and I would much rather have the BS enclosed on both sides by a tall cabinet or boxed-in by corners for a nicely-appointed-look.