You might consider planning each day's route like a kid applying to college, a realistic goal, a safety goal, and a reach. Realistic is based on what you can do, safety is for when you have a stomach bug, or two flats, or get really lost, reach is when you feel great, have a tailwind, and channel your inner TDF rider. Sounds like fun, in addition to the advice to do hills, practice with your load, or equivalent, to get the feel of the bike, and your legs with a load.