When will panels / concerts / keynote / exhibitors be announced?
Soon. Don't expect any definite announcements any sooner than 4-6 weeks before PAX. Don't expect a final schedule and show map until about two weeks before PAX. If you're curious if your favourite game developer, journalist, internet personality is going to be there, shoot them an e-mail and ask.
Are the theatres cleared in-between panels / concerts?
YES, we empty each theatre between events unless explicitly stated otherwise. We feel this allows the most people to experience content at the show.