Backsplash tile - spacing electric boxes
I use standard 1/2" plaster rings and then just use longer 6-32 screws when you're installing the outlets. If you really want you could use 5/8" plaster rings but it's not necessary. When you tile, you need to make sure you're close enough when cutting around the openings so the ears on the outlets will sit on the tile. Once you do one, you'll get the hang of it. I'd suggest to have an outlet handy (NOT hooked up to the AC yet) and place it in your opening while tiling to make sure you have proper clearances. Also, if you have a GFI style outlet, you'll need to make sure the screws for the cover can recess deep enough behind the tile. See picture. See how the screw hole for the toggle switch is within the opening but the screw hole for the GFI cover is way at the end? So if the ears of the GFI are OVER the tile and you try to screw the cover on, the screw cannot go into the tile so you won't be able to get the screw all the way in. You need to make a small notch on the tile so the screw can be pulled in past the face of the tile. You have to be careful you don't make the notch so big that the cover can't hide it. Like I said, lay the stuff out BEFORE hand so you fully understand what I mean. If you don't and and fail to make that notch, you won't be able to completely screw the cover on and it will look like pooh.
As for the tile, yes you can go directly over the drywall. I use a modified thinset like Ultraflex II. Make sure your first row up from the counter is level. If the counters aren't level, keep the uneven line between the counter and the bottom of the tile. You'll caulk that line anyway. Also use caulk if you have a 90° corner. Some will say you can use mastic for the tile. You can but I'm not a fan of it. I spend the extra few minutes to just mix some thinset and it's all good. Mastic and water don't mix so even though a back splash is technically not a wet location, I play it on the safe side.
Good luck. Take and post pics for us!