is the seating first come first serve?

No...You have to reserve your seat...

There are only a few general admission theaters left out there. Most have committed to reserve seating... it's just better for everybody. Btw, AMC 20 is reserve seating. Enjoy your show!

I booked tickets in advance. And you may not know if the seat you want to sit in is already taken

Incorrect. It is first come first serve if it is like a movie where it didnt come out recently. But sometimes if it came out and its popular u choose ur seat at ticket admissions.

Yes

Yes, seating is based on first come first serve basis