BMS does not mean any standardized component doing a certain thing. BMS can do anything, or may not do anything at all. It very likely does something else than you expect. The three letters alone are meaningless.
You need:
1) the full documentation of the BMS,
2) to understand it
It will also answer all of your questions.
Before that, there is no way to make any assumptions about the system.
Practically, there are three common classes of BMS:
1) Those that monitor and inform you, and you are responsible for implementing the required disconnect switches.
2) Those that do include switches internally, so that the pack terminals are protected against overcharge and overdischarge; but the voltage/current/temperature limits are beyond normal operating limits, only as last-resort safety. You need to implement another layer of BMS for good safety and good cell life.
3) Like 2, but with limits chosen within designed operating ranges of the cells; this is the only type of BMS that acts like an "ideal battery" which you can just use.
Without the documentation, guessing is meaningless.
Balancing is completely irrelevant question. You are ready to go when you understand why I say that. You need the basic understanding of the li-ion cell operating limits, and how the packs are managed to see this.