You can patch by screwing a piece of wood onto the existing ceiling. Just cut longer bits than the hole itself and by keeping it tight screw on edges. Then you have a new framework for a patch which can be attached to it. Of course the wooden piece would be on the inside part of the existing...
Hi
It is unfortunately common in modern times to use fancy paints from leading brands. I have always used matt paint for the surfaces and it has never been problems with it.
As mentioned before, use a mist coat of cheap matt paint over a new plaster for it to soak the moisture. This will...