When you want smooth walls that are easy to finish.
You cannot use sheetrock as flooring, period. If you meant on a wall, there is no reason you cannot put sheetrock over tiles. The question is why would you want to! Why not remove tiles and material behind, which is probably sheetrock, and then install new sheetrock. If it is an area prone to moisture you could use moisture resistant sheetrock. The job would look better and you would not lose the space by adding over existing material.
You can use drywall nails or drywall screws. I prefer the screws.
No, you can use other materials.
Regular mud.
Sheetrock, drywall or gypsum are insulators.
Yes, sheetrock is fire resistant.
should you install sheetrock horizontal or vertical
No it will actually ruin your Sheetrock or Drywall
it just adds lime to the soil. I will help if you need lime.
I would use about a 5 pound bucket. It all depends how far apart your sheets are and how good a mudder you are.
yes
You don't need a drill bit for anything on drywall.