Can you explore the grounds during the haunts? Does the mayflower after dark have actors or is it a walk through?

Yes its a walk through..the mayflower is the only building on premise that you can actually take pics of..a lot of history has happened in this corridor so certainly do your research on pennhurst if you haven't and watch the documentary as there's a lot of footage in this building that's in that documentary...its called suffer the little children, very intriguing and I'm just going to put this out there I just returned Fri. From my yearly visit to pennhurst and a lot has been added this year to the attraction so I ghighly recommend it as usual..and for definitive answer no actors in mayflower you explore the designated areas at your own pace

Historical walkthrough similar to a museum. With exhibits and the ability to take photos of various rooms

It's a walk through only. Very cool experience.

Yea, I have been there inside yesterday on the 14th of October 2017, and no, I have not seen any supernatural scenes or happenings, however I saw markings, and nobody checked the stairs by the end of the museum near the exit, their was a room their I went inside, and it was extremely Hot, almost like an oven. But no spirits. Still it was fun, their was no actors, or maybe I saw one, he looked old, like in his 40s.

The Mayflower is a walk through wth no actors. I do not believe that security allows walking the grounds. Only when guided tours are given are you aloud anywhere off the roped areas.