KazzyK810,
Thank you for your reply!
Choco and I flew without much trouble last week. US Airways made everything easy for us.
As you mentioned, I purchased an extra seat under my name for $40 instead of carrying him on as a pet. (I take an air shuttle, so an extra seat is much cheaper than the pet fee.)
Just in case, I also got the health certificate; I visited PAWS Wellness Clinic and paid ~$35 for the basic health exam, rabies shot, and the health certificate. I love this place! No one asked me to show the document, but it was just comforting to have everything ready.