To your points:
1. "Guys" means "everyone" in the midwest -- boys, girls, dogs, etc. I say, "Come on you guys, get in the house" when trying to round up my dogs. I live in Indiana.
4. More audio could be the girl's voices. If so, I thank LE for the editing.

I really don't want to hear their fear.
6. I feel LE know who he is and knows he lives or has family in the area (they expected he may have returned to celebrate Easter with family).
I wonder if the car they are seeking was borrowed. Since I feel they know who the BG is, the car isn't directly connected to him but may have been borrowed. I think they are hoping the person that owns the car will remember loaning it to BG and come forward.
I am also wondering if the younger sketch was discounted due to a false alibi and now LE realizes it.
I don't think it was someone the girls knew or respected or Libby wouldn't have felt the uneasiness to begin recording. They were creeped out by him.
I am confused though -- do they or don't they have DNA?
JMO and thoughts...