Using multiple accounts using the same IP address won't count to the total amount of mice when regarding these limits.
Any changes to the mice amount doesn't take effect until the next round. For example, if there are 49 mice in the room, and during the round an extra mouse joins resulting in there being 50 mice, the mice's clothing doesn't get hidden until the next round, i.e. if there still are 50 mice in the room next round.
These are the total amount of mice. 11 mice means 11 mice including you.
In order for the "Cheese gathered first" stat to increase, there needs to be 11 mice in the room.
Once there are 50 or above mice in the room, all of the mice's outfits gets hidden. This is to reduce lag in overpopulated rooms.
The bootcamp stat does not increase unless there are 5 or more mice in the room. Also, the bootcamp stat does not increase the first time you beat a bootcamp map in one bootcamp room. This is to prevent "room-hopping." (Read more here.)