I love the look of a full wall of tiles. Have you considered going with larger format subways instead of small? We used 4x12 subways and I like the less busy look, but our kitchen is much smaller than yours. I think if you are going to leave things relatively simple as it is now, you would be fine with the smaller tile.

Smaller tiles have a richer look IMO. I would definitely go full wall with the backsplash. It will look terrific.

I'd go full wall. My personal preference is larger tile, but I think all would look nice!