1. Even if a game is a "regular...it's at the same place/same time/every blah blah blah"...they tend to be still posted up as a notice for each distinct game, each with its own sign up, etc...
2. Anywhere from a year to just a couple of days. Obviously the more organized milsims tend to have longer notice periods...but even still some "good ones" get filled (aka capped) really, really quickly.
3. There is definitely a slow down...but there are still games outdoors. You'll find more indoor games once the snow hits the ground and stays.