Best adhesive I've ever used for mosaics has been Bal's Mosaic Fix.
Walls must be in very good condition and flat to fix them propperly.
For cutting small mosaics you can use nippers and the wet cutter.
When fixing them to the walls watch for excess adhesive seeping through the grout lines, as this can be a very labour intensive job to clean up.
To avoid this "depending on the mosaic size", use a 3mm trowel for the adhesive and gently press the tiles to the wall with something large and flat to get an even finish.
Good luck with it
