Just letting you know that a metal pressed splash back is only suitable if powder coated or left galvanized. It does not meet regulations when painted as the paint is not fire rated. Powder coating is. If you do it yourself, no one will know, but it is likely to dis-colour, blister or even singe! Powder coating does not make it easier to clean. But if you were really concerned about cleaning it you would avoid it all together. The recommendations above solve that easily. At the end of the day, a gloss finish will make spraying and wiping the grease, steam and fat away easily than a satin or Matt surface. Glossier the better, powder coat can control that.

My two cents worth would be to extend the tiles to cover everything below the canopy of the extractor (could go higher but that would be the minimum) and use that as your level on the other wall. So you ignore the curved glass (I assume that that's kind of the point of being transparent) and go with the straight edges of the tiles. You certainly wouldn't want a funny little segment of painted wall below the curved glass – it will look awkward and be very difficult to keep clean. My remaining concern is – have you already installed the rangehood or can it be easily taken back down to allow the tiler to do a really good, neat job and then the rangehood can be installed nice and tight against the tiles?

Forget subways, really overdone & can look so cheap. The more grout you have the more cleaning you'll have to do. It collects grime ( known in the trade as 'grotty grout' ) & is hard to maintain. Go for glass, the possibilities are endless, from sophisticated plain to funky patterned. Easy care & long lasting. Personalise your space, it looks really fab, love all your drawers, so practical ! Would love to see the end result. Please post pics.

You will have to remove to repair, and then it might break anyway. Re-asses once the mirror is off the wall, as to whether the glass can be re-silvered to form a complete mirror again, or whether the glass is too damaged.