Your questions have pretty much been answered, but I'll add the same.
You check in towards on the left side of the front entrance and congregate just outside the left tunnel under the train station. This group will be EMM and PPO ADR guests.
This was at 7:29AM a few weeks ago:
View attachment 337490
They let you in approx 7:45am. Approx being the key word.
On the opposite entrance to this, regular guests are also congregating, as they are let in and free to roam Main Street/the Hub until the park opens at 9AM. There aren't typically very many people there at this point, but there will be some.
I have seen it where both the EMM/PPO group and the regular day guest group are let in at the same time, and I have seen it where the regular day guest group is held for a few minutes and the EMM/PPO group goes first. I'd say YMMV in this particular aspect as things can change on any given MK morning.
Hope that helps and also hope you have a great time at EMM.