Generally the format(1 game v. 3 game), is the first matter discussed. It hard to negotiate anything else without knowing this.
Once that is decided everything else is on the table. Typically location (home/home/home, home/home/neutral, home neutrals, all three neutral, etc.), if neutral whose home when, game times, umpire chapters and crew format, game balls, etc.
The REAL negotiation is for the 1 v. 3 game series. The coach wanting 3 can concede any and every thing in an attempt to get the series. If it doesn't work and he loses the flip the negotiations typically turn very cold.
It's about the most interesting off the field aspect of the playoffs to me, and almost as much fun to strategize about as the games.