Share a PPT presentation in full screen/no audience; then full audience for Q&A

Hi

I am hosting a meeting for over 100 people to review a powerpoint presentation.  

1. I'd like attendees to enter the meeting without my having to admit them because there are too many people.  

2. I'd like to show a full screen (no slides in the queue nor attendees being seen).  

3. After the presentation, I'd like to exit the presentation and allow video of all attendees for Q&A.

BJC80