Spot On Building Contractors

Yes framework should always be painted and allow drying time before hanging doors

You will need to use a mitre saw preferably, but double check the internal corners are square using a set square.

Firstly any cuts or adjustment made to a door should be done equally , for instance planing 20mm from a door should be ideally done by taking 10mm off each side .
best way or the way i adjust a door is to rub a bit of chalk down the door frame edge and close the door, the chalk will hit the door in the tight spots and this is where the door will need planing.
sinking the hinges further into the door frame will cause issues with opening and closing . i generally hang a door with 5 mm clearance all the way around .

This would require being stripped back , i would treat with 2 coats of sbr then repaint with the appropriate external paint .

This would need to be carried out by a professional, calculations would be required to make sure all the treads and risers were fitted correctly and safe.