1: The grade at which you "max out" is called your journeyman. It is generally a GS 13 or 12 for 1811s. The next grade is generally a supervisor. For us, sups are GS13, journeyman is a 12. Many get their feathers ruffled when they hear this. However, unlike other 1811s we still get some OT with our LEAP. 
To get promoted to a supervisor, you must compete for it. For us, take a merit promotion exam and then submit a promotion package. Same goes for Assistant Chief and Chief jobs after that.
2: You cannot be forced to promote. The only way I see being "forced" is when you see no other alternative than put in or be managed by a loser that you think may get it. LOL But the jobs are announced nationwaide, so this is not a huge concern.
We bring evil things to evil people, kicking in a door near you!
."In theory, there is no difference between theory and practice. But,
in practice, there is."
- Jan L.A. van de Snepscheut
"The difference between 'involvement' and 'commitment' is like
an eggs-and-ham breakfast: the chicken was 'involved' - the pig
was'committed'."
-unknown
Working on a PhD in CQB one doorway at a time.
When the wolf attacks, he will find not all who run with the flock are sheep!