FNAF1 and 2 nightshifts start at midnight, and there's already no one in the building. MM takes place at midnight, hence the name. And there are a lot more cars on the parking lot, than just the stuff. It's obvious that the place is open for customers.
Just because this is the case for a few weeks over the course of 10 years and many different locations doesn't mean it's a rule for every other night Freddy's has existed.
Nothing implying that that it's not a bouncer.
Nothing implying it isn't the FNAF 2 location either.
Not really. Establishing William as a drinker would flesh him out more. As for deep meaning.
There are lots of ways to flesh William out more, and most do not revolve around this scene.
It's really not. People are split between 1983 and 1985, and I'd even say that 1985 camp is bigger (example).
I say Cassidy for sure in 1983 for a lot of reasons I don't want to list. Susie and Cassidy are first which matches what FNAF 1 newspapers say about two kids going missing initially. Everyone else as I said could happen theoretically in 1985 which as the newspapers say bumps it up to 5 total.
FNAF4 gameplay is heavily inspired by FNAF1.
FNAF locations can be open and closed multiple times. FNAF 1's location can be open in 1983 and 1993 later on. This is a concept that is important to understanding any timeline. Regardless, I say it doesn't matter because that's a weak connection to be honest.
Mike draws Nightmare Fredbear as his "recent dream" in the logbook.
FNAF1 Phone Guy call is heard in FNAF4 gameplay.
This is definitely a bit hard to explain and a requires lot of theorizing.
In my opinion, there are multiple spirits and people writing in the book, not just one. Many people think that the book is trying to talk to Michael, but I think it's Michael using the book to try and talk to CC. This is why you see the writer asking questions to CC about stuff a brother would know to see if he's there. The reason you see Fredbear here is that Michael is asking CC if he still has the same nightmares as before in 1983. CC responds by saying yes through drawing Fredbear,
Regardless of who is writing in the logbook and who is having the nightmares, the dream being recent doesn't stop it from being a old dream as well. I don't think anyone has intense nightmares like this that just go away, so CC can still have them in 1993. CC would've heard these phone calls if he was present as a spirit or with Michael during FNAF 1. The dreams may change overtime to match FNAF 1 gameplay, but the CC has probably had them since 1983.