It is safe to install panels of drywall on side walls by yourself. However, if you are installing drywall on the ceiling by yourself, you will need a drywall lift to assist you. Attempting to put drywall on the ceiling without a lift is extremely dangerous and difficult.
Yes, it is safe to install drywall yourself. Make sure that you obtain any necessary permits and wear protective gear and supplies to prevent from inhaling any dust.
contracts to install and finish drywall for companies and individuals
If by top layer you mean the paper, then re-install drywall on that wall.
They install drywall, sometimes tape and mud it also, although commercially that is a more specialised job.
Plastic sheeting works well for this, and yes it goes behind the drywall on exterior walls to help prevent moisture from getting to the drywall.
Yes, many people do that.
The drywall anchors are designed to prevent any damage to the walls. This is the best way to install these shelves without any damage at all.
Yes, you can by using standard tile adhesive.
Yes, you can.
No, but it should be securely covered by heavy canvas dropcloths.
A bit costly but sure knock yourself out
Try doing something to distract yourself. -ebush another view: find out if your body is deficient of something found in drywall (if that is possible): find a very big rubber band and put it around your wrist and every time you think about drywall, snap yourself really hard.
As safe as they are installed against any surface. If installed corrected they are very safe.