On the condensation, because it is not a side issue and it will decide whether the film is a good idea.
Water appears on the glass because that surface is the coldest thing in the room and the air touching it cools below the point where it can hold what it is carrying. Two variables, and you can attack either: how cold the surface is, and how much moisture is in the room air.
Insulating the glass raises the surface temperature, which genuinely reduces it. But if the room is producing a lot of moisture, all you have done is move the coldest surface somewhere else — the reveal, the corner of the ceiling, the outside wall behind the wardrobe. Those places do not get wiped every morning, which is how a visible condensation problem becomes an invisible one.
So it is worth knowing where the moisture is coming from before sealing anything. In a flat it is usually drying laundry indoors, showers without an extractor that actually reaches outside, and cooking without a lid. Those are all much bigger sources than people assume, and the first one is enormous.
The combination that works is insulate and ventilate, and they sound contradictory but are not: you want less heat leaving and less moisture staying. Short sharp airing beats leaving something ajar all day, because you are trying to swap the air without cooling the walls.