Because of the light switch on one wall, I'd be tempted to not tile either side wall, to just leave it as it is now. I'm puzzled as to what the first photo is showing? Is that a level?

I would not tile any more. Looks great, as is. caulk it and paint.

Not sure what the 2nd picture is showing but I'd just tile the back wall, leave as is now.

If you are adding a light rail to the adjacent side wall?! Do NOT!! : )

What 2.5 inches where please?

@Lyn Nielson @lisedv @JAN MOYER I think OP is referring to this side wall being bowed and the resulting space where countertop meets the wall. Are you suggesting it be filled in with caulk and just paint the wall?

Jan, she said a quarter of an inch (.25”) NOT two and a half inches (2.5”)

Yes, @bearbev unless they apply a skim coat of mud to the sheetrocked wall to add the .25 . A clean bead of caulk to finish it, and paint a straight line over the caulk to clean it up.

less noticeable than a jolly or trim piece that will draw attention to it.

I think the tile should only be on the back wall - don't extend it on the side walls. Looks great as it is right now!