If taking the discs off then impact driver (the type you hot with a hammer) to undo the screws if they are tight. When you refit apply plenty of grease (I do use copper slip for those).
get a wire brush and clean up all the calipers. But be careful around any piston seals (I use a nylon brush around there). Also get yourself some brake cleaner.
You may also need thread lock for the caliper bolts (the blue prit-stick style loctite one from halfords is very good).
Fortunatley discs aren’t expensive and are even easier to change than the pads.
depends on the car, some are. And as for easy it depends on if the person who fitted them put enough anti-seize on the disc screws.
Don’t forget brake fluid needs changing every couple of years too.