Q: First, when you go to play, how are the gametypes decided? Is it cast to a vote? Is it decided the week before? Or does a Field Marshall (or someone in charge at the field)
A: usually the game marshall will decide.
Q: what type of game will be played? In addition, what are the most favoured game types? Military simulation? Team Deathmatch?
A: each field is different. Every game Marshall thinks of his or her own game styles. But they mostly involve team elimination, attack and defend. The field I play at has a game called black box, and that's usually the favourite.
Q: how long do games typically last?
A: a typical day is about 4 hours. That will include 4 plus games. There's other milsim games that are anywhere from 4 - 24 hours.
Q: is there a minimum (or maximum) number of players allowed to play at one time?
A: for a walk on there is no minimum or max number of players. But for the large milsim games there is a cap, which will be in the game description.