First, welcome to the forum. You have come to the right place for information on all things Airstream.
About the floor replacement...I've not done it, but went to a seminar a while back at a rally, and the main thing that I remember of the procedure was to replace one piece of the plywood at a time.
Additionally, if I were doing it, I believe I'd put a sealer on the wood to reduce the chance of floor rot in the future, but this is just my thought.
Good luck with your projects and I'm sure more knowledgable and experienced restorers will chime in soon.