FLOOR: I have plans for floor warming system > self leveling compound > un-modified thinset > Ditra > un-modified thinset > slate tiles 6x12". I have read the Schluter Ditra Handbook, and on page 13 there are instructions that fit my situation, as outlined above.

WALLS: For my walls I will prep with HydroBan, then use a thinset to apply the 4x4 ceramic tiles and a listello of white carrara marble tiles.

Un-Modified thinsets...I have read that Laticrete 317, Mapei Kerabond, and Ditra-set are all good un-modified thinsets.

Modified thinsets...I was thinking of getting Laticrete 255 for use on my wall tiles.

I understand that the unmodified is a setting type thinset and cures chemically. I have read that modified needs air to dry.

Questions:
1) Which unmodified thinset do you prefer?
2) Is is better to use modified or unmodified thinset on my walls?
3) Which modified thinset do you prefer?
4) Because of the whitish marble do you recommend white thinset for the walls?

Thanks for your time.