Welcome and good luck.
I started cycling again at age 53, about your size. Just ride a lot and keep adding more mileage, and hills if you're going to be in hilly country. I don't know what the weather conditions on your ride will be like- but I would imagine more hot and humid, so you'll want to get some help on how to ride in those conditions. Lots of water, I'm sure.

Good luck and keep us posted as you get ready for the big adventure!