History:
Been trading for 15 years
Answers:
You would be better off taking the panels out and tiling onto the wall in my opinion anyway any more questions then let me know
No definitely got some sort of leak where water is escaping hence the reason why the tile is coming away from the wall or it has not been prepped properly before tiling or water is escaping from somewhere it needs to be done asap before it gets any worse
Ideally a week but you can tell when the plaster is dry enough to paint on
I would give them a quick sand with sandpaper so it's nicely prepped before painting
The plaster should of been painted with summit like a miscoat first then finish with your finished colour choice