Newbie-ish Question: Do Points or Points/Cash stays count towards current Megabonus free night after 2 paid stays?
No they do not, unfortunately. You will not get night credit staying with points or any form of reward.
If you want to do cash/points, make sure you make 2 separate ressies, so that you get credit for the paid stay.
If you combine a free night(s) with a paid night(s) you WILL get credit for fully paid nights, even if it's on the same reservation. For example, if you have a megabonus reward night and you are staying two nights and use the megabonus reward for one of those nights you'll get credit for the other night.