Watch out at doors between rooms. Should have movement/expansion joints there. Each area of screed can shrink towards it's own centre cracking where the meet. Has happened to us.
No.
In theory it is possible for planning permission to be cancelled but it virtually never happens because the council are liable for damages. Would certainly never happen in a situation like yours.
I suspect the BCO may want a ball 450mm in diameter to fit through it. Not literally (that's not in the regs) but by measurement.
We have a window a fraction too narrow but the BCO allowed it provided we fitted a thicker more fire rated door to that room.
Google says..
Minimum Dimensions: Both the clear opening width and height must be at least 450mm.
Total Area: The clear openable area must be at least 0.33m^2. If you make the opening width the minimum 450mm, the height must be at least 735mm to 750mm to hit the area required.
Height: The bottom of the openable area should be no more than 1,100mm (1.1m) above the internal floor level for safe access.
LED lighting creating crisis for human mitochondria: Researchers..
https://www.newsnationnow.com/health/led-lighting-human-mitochondria-research/amp/
So presumably warm white is better for you than cold whilte.
Make sure you understand the rules. Labor should be zero rated to you not charged and reclaimed. Supply and fit should also all be zero rated to you (both labor and materials). Only the VAT on materials you purchase can be reclaimed.
If you get quotes (for example for plastering) that includes VAT its best to ask them to revise the quote before you accept it. Any problems refer to the VAT notice.