As much as possible, we will play full field lacrosse! As long as we have 10 guys per side and two goalies and/or tarps, we will play regulation lacrosse. If our numbers are smaller or if the 20 or so guys there decide they don't want to run, we will play a shorter field modified game.
We won't run a game clock. Basically we can play until nobody is left, the sun goes down, or the person with access to storing the goals has to leave - whichever comes first. Although if we don't have goals, we can always play Ultimate Lacrosse or something...
We will have them - at least opening face offs. Decisions will be made at each session whether to have face offs after goals. Since most people seem to be in favor of facing off as frequently as possible, this should be acceptable. The alternative is possession behind the net (similar to basketball).
With the pick up nature of the league, we may or may not have a half time. There will probably be a full water break after which teams switch sides. If so, there will be an opening face off to start the new "half."