"Do i need a water pressure regulator?"
Maybe, maybe not. I don't have one, and have never had any problems. If the RV park you are in has VERY high water pressure, you may need one.
"The nights are supposed to be in the upper 20's. I assume I need to disconnect the outside hose from the camper?"
While perhaps not totally necessary (it is doubtful that the ice will expand enough at those temps to damage the hose), it is not a bad idea to disconnect and drain (if you are going to leave water in it, why bother to disconnect it?) the hose. Be sure there is enough water in the tank for nighttime needs.
have fun.