The backsplash is finished and installed and it looks like this:
I ended up hanging it all in one piece, as it was just manageable in terms of weight.
I’m glad that in my research I came across the suggestion to fill in the spaces between the tiles with sand before applying Thinset adhesive to the back – this worked really well to prevent any cement from being pushed too far forward between the tiles.
After I slathered on the Thinset to even out the difference in tile height and attached the mesh, I put another piece of plywood on top, thinking it will keep pressing on the whole thing and levelling it out. This was not a good idea.
When I returned the next day, ready to start working on the next stage of the process, it turned out that the board I put on top prevented the Thinset from drying properly. I had to wait a few more hours while the thing stood uncovered and dried, which still was not enough time to for it to dry thoroughly. It worked out ok, but it would’ve been better if I left it for another full night.
After seeing it this way, I decided to use sand-coloured grout! *Sigh* I didn’t like it as much as when it was actual sand.
Anyway, there was also a lot of sand to clean up after the plastic came off.