18 inches to center
12 inches from the center of the drain to the back wall behind the tank. Some toilets are 10" rough in. Also should be 18" from side wall to center of toilet if possible.
12" from rear wall....16 to 18 from side wall....measurements are to center of flange
A standard toilet roughs in at 12" from the wall.
Would be risking damage to the tank and possibly open for a major lawsuit
Code minimum 15" to center of toilet from side wall.
18" max from side wall to center.
21"
The toilet flange is installed 12" from the FINISHED wall surface to the center of the flange, and 16" (residential), or 18" from the finished wall to center of the flange in commercial,or wheelchair accessible applications.
24"
It is not a problem at all. But you will have a 2" gap between the back of the tank and the finished wall.
Standard height is 15" but you can get comfort height or ADA models which are 17" high. The standard toilet rough in dimension is 12", which means the outlet of the toilet at the floor is 12" from the unfinished wall, but they do make 10" and 14" rough in models. The width really depends on the type of toilet you get but remember International Plumbing Code requires 15" from the center of the toilet to the nearest wall. Hope that helps.
12" on center from the back wall, 18" from the wall on the side(s).