First remove the paint around the rusted area, grind down the rusted spot, then paint over the spot and cover the rest of your car you don't wish to paint with something like newspaper.
Scrape then repaint
Depending on the seriousness of the damage, car repair insurances will either repair the whole car (if the damage is minor), or only repair part of the car. Parts that are usually not repaired are the headlights and windows.
There is no rust remover that going to repair the rust that has accumulated on a car for that long. It will be best to have the floor repaired by a professional.
If the rust is only on the outside of the microwave you can wipe it down with a cleaning agent for rust. If it is on the inside mechanics, you can not remove it without damage.
you can learn how at the attached link.
The best product to remove rust is limeaway. That stuff will remove anything staining including rust. It will not damage the actual item that was rusted. Only the rust will be removed.
You can't really repair the plastic on a car you have to replace the part. If you were to try and repair it you could use bondo but it wouldn't look as nice.
Rust hole repair at body shops tend to be expensive repairs. The exact cost will depend on the area, the shop, and the composition of the car body but these repairs average approximately 1000 dollars.
This answer depends on what damage the undercarriage has. If it is just minimal rust the it can be left with some anti rust protectant. If it is bent a body shop will need to attempt to straighten it out.
While it might be possible to fix, it is usually not worth the expense. Snapped from rust, previous damage, prior wreck damange with bad repair, whatever the cause, it's time to retire it.
The repair of damage caused to your car when you caused the accident
I don't think you are able to fix this rust problem, take you car to your local repair shop or car dealer. They should be able to take care of your problem and fix it for you. Hope I can help.