You are on the right forum for answers to your questions. I am not knowledgeable about all the new bikes on the market. I would not try to tell you which bike to buy, other than to say any well made touring bike that fits you right and is made to carry racks and gear should meet all your requirements. I have cycled the southern tier a number of times, and the PCBR once, and a little more. There should be some pretty good books on bicycle touring in the library, or through the library. Crazyguyonabike.com is a good place to look for information. Google around and you will find more information.
You might want to ask specific questions. There are people here with detailed, intricate knowledge of matters to do with bicycling, and with various kinds of gear. As for myself, I have bicycled about 34,000 miles through nineteen countries. I can tell you about bicycle touring in general, and what you might experience on the road. I have been to Saint Augustine. I was born and raised in Florida.
In a broad general way of giving advice, you could follow ACA's ST route to El Paso or points farther west. Then go north to intercept the Transam route near Pueblo, and follow it to the west coast, or go by way of the western express. Leaving FL you can take the gulf route or highway 90. The gulf road is flat, mostly. 90 is rolling to somewhat hilly, and can be relatively level here and there. It is my understanding that if you get those ACA maps, you have a good deal of your needed information problem beat from the get go.
