Best adhesive for small marble tiles

[philipio]

Good day all. My daughter has asked me to tile a cooker splashback in her kitchen. They've chosen marble tiles of about 150mm x 75mm x 8-10mm. They're quite chunky things for small tiles. The wall they're going on has been sanded back to smooth brown finishing plaster and the wall itself is solid (ie not a stud wall). As only a DIY tiler, I have a couple of questions for the experts on here who I've received excellent advice from on previous occasions . . .

1. Does the wall need any preparation prior to tiling?
2. What's the best adhesive to use for this kind of tile?
3. What would be the most attractive spacing gap between tiles?
4. Any other considerations?

The whole area to be tiled, although rectangular, is probably no more than 1 square metre.

As per previous occasions, many thanks in advance for any forthcoming advice.

 

[ltppebbs]

Marble tiles will be a nightmare as a splashback behind a cooker, as they will need to be sealed.
Any hot fat from cooking will burn through the sealer leaving oil marks over time, cleaning will be a mare too as any cleaners with bleach or acids (which is pretty much all cleaners from a supermarket) will break the sealer down very quickly if its not cleaned with a ph neutral cleaner.
Iwould suggest they go for a porcelain look a like marble if its not too late.