In relation to the floor, I would say that if its just in the hallway area, the 30mm insulation would be sufficient (assuming that you're not going with underfloor heating.)
You need the 3'' if screed to ensure that it is strong enough, but then again, the tile on top will be taking most of the pressure.
But it looks like you have to reduce either the insulation or the screed, I'd reduce the insulation, if only in that particular area.
Although a two inch screed covered with a tile may not be a bad option either.
As for the damp patch, you seem to have looked at the problem being water coming in somewhere around the window, which you thought you had sorted out, but it's back again, frustrating alright.
Could it be that your damp proof course is compromised under this part of the wall, or is moisture finding its way in through the ground?
Otherwise I suppose its just a case of looking around the window again if you're convinced that there lies the problem, and resealing it all around.