If it's mechanical then it should physically pull the lock to unlock for that door.
Electrical means it just a switch that triggers the central locking - useless with a dead battery.
Not quite sure how a loose driveshaft nut would sound like noise discs.
Either way you were very lucky, that nut literally holds the whole wheel and hub on the car. You may even have damaged the bearing by having it loose.
Sticky calipers can also cause squealing as the binding heats the disc too much and pads cant retract easily.
It might be contraversial, but I still put copper grease on the back of pads to help prevent squealing, though there are those now that claim it's very bad. 25 years on of doing and...
Usually it's the passenger side since the fan usually sits up at the scuttle panel, and more room on the passenger side. Cans say for sureon the micra as I've never take the fan out.
The air is taken in up at the scuttle panel, should be no direct access of air from the engine bay.
It'll depend on the alloy, if the seat matches the bolt then it should be ok.
20mm should be ok since that are M12. Depends how thick the disc is, but I'd guess should get a good 15mm, so 10 turns of the bolt.
New users could have to wait for approval.
Sign up could have improved human checks, even dumb questions like "how many wheels for the micra have" will beat spam bots (and probably the users that shouldn't be posting too!!!! ;) )