Tile – kitchen backsplash tile grout or caulking

You can put it onto the drywall. You want it smooth and to not have a glaze, so you may have to sand it. If its been painted with a topcoat, you may want to paint it again with a primer.

Use mortor that is specifically designed for glass tiles, not ceramic tiles.

I spend a lot of time in France and in the midwest US.

Customary in France if you put up a backsplash is to extend it before putting up cabinets. There is no caulking usually between the backsplash and the cabinets.

Also the cabinets would be floating on the bottom most of the time. And the bottom cabinets are on legs - where in America they are almost always enclosed. Maybe this allows any leakage from backsplash to hit the floor easy.

It is just a different way of doing things because people are accustomed to taking their cabinets and everything with them when they move. I have seen this trend slowly change over the past 10-15 years though in that you will walk into some apartments or houses now with the kitchens already done but this is not the norm.

And obviously you do the backsplash last in the US because we like everything permanent looking. You use less tile and it is just easier to do that. Also - and just my opinion - but homes in the US are built... lets say faster. So you don't always have right angles, your floors are slanted a little, the walls wave a little... Meaning that it looks better to have shimmed cabinets. I have installed IKEA cabinets in kitchens in the US and people look at me like I need to fix their walls when the cabinets don't sit flush.

Personally I think it would be good to do a little of both. First it is kind of dumb to take your kitchen with you - which may not work in your next space and then you sell off pieces for a fraction of what you paid. But I am also a huge huge fan of keeping lowers on legs and having more mobility in your cabinets.