Major bath remodel

[workbee]

Maybe this question is not for this part of the forum, but here goes and excuse me if it is. I am planning a bathroom remodel. The bathroom is old(35+yrs), on the second floor of my house. The mosaic tile present on the floor has been glued directly to the plywood and the floor is uneven because of moisture(have had several toilet overflows-kids). The tile on the walls is 4x4 and comes to about 2/3 of the wall-glued to regular sheetrock. There is no exaust fan. I am for a complete demo including the floor and install a new subfloor. Since it is a small bathroom(@60sq ft) I would like to put in warmboard. Is that enough for a new subfloor? Or do I need something underneath. The walls I would either do hardibacker/cementboard all the way to the ceiling. Tile is going all the way to the ceiling/ densarmor on ceiling.
Several questions:
1) Should I use Ditra on floor and Kerdi on walls over the warmboard/hardibacker or is this overkill?
2) Tub will be installed-tile underneath or no?
3) Awning window will be installed where tub will be-good idea or possible future problems?

Thanks for any suggestions.

[Floorguy]

1.) Ditra on the floor is a good idea. Way better then cement panels. You don't need the Kerdi, unless your in a shower, or tub surround.

2.) No tile under the tub. But when your setting tiles, it is a good Idea to fill the tub, while setting around it.

3.) Sounds good to me. I want one!! Or should I say, The wife wants one!!

[workbee]

Thanks floorguy!