im planning on running with some friends, what are the rules on coop? any difficulty or easy only, what friendly fire mode? regular or hardcore ill be running today on easy and reg ff but will rerun if told those arent good

Whatever settings are fastest for you.

Lower difficulty makes aliens weaker but also makes marines run slower, so Brutal difficulty is theoretically fastest if you can survive it. And on some maps, Onslaught can be useful to spawn shield bugs in useful locations.