Bathroom tiling questions

[nick9one1]

I'm about to tile my bathroom and have a few questions.

The floor is T&G with a thin layer of plywood (I will remove this).
the bathroom was previously tiled from floor to 1/2 way and the top painted with bathroom paint.

At another property I once had a badly cracked tiled floor and want to avoid this.

Q's

1. What is the best brand/type of backer board e.g. cement/fibre?
2. I've seen 6mm and 12mm available, which should I use?
3. Is it worth laying Schluter Ditra over the backer?
4. What is the best way to prepare the painted walls prior to tiling? is there a product available, or is it a case of sanding/scoring?

Thanks!

 

[ktuludays]

We always use 6mm no more ply or tile backer board on bathroom floors and a good powdered flexible adhesive. No call backs in 5 years of doing this.