If you read some journals over at crazyguyonabike.com, you'll start to get a feel for how far you might ride in a day. There are lots of journals over there, so find ones by someone of a similar age and condition, and who seems to tour in a style that suits you. That'll give you an idea of how far you might go in a day. Most people go from 30 to 90 miles in a day, with a pretty big concentration in the 50 to 60 mile range. Use that as a starting point. Then figure out if you might like to take days off or not and how often. Use the maps to figure out if there are particular attractions you might like to linger at. These factors can give you a rough schedule.
Now look at your maps. I like to make a list of all the places that are consistent with the types of places I like to stay. Note how far apart they are. From this, you can make a rough plan, but don't feel compelled to stick to it. Take the list with you so that you can find alternatives along the way. Perhaps you are getting tired early--look at your list to see what's coming up next. Maybe you get to your tentative destination and find that it's a dump, or maybe you just feel like riding farther--look at your list again and see what's farther up ahead. Can you get there?
I usually plan one day at a time. In the morning, or the evening before, I pick out a target for the day. Most of the time, that's where I end up, but I remain flexible.
If you have a hard stop, such as a non-refundable airline ticket home, you may want to make a tentative schedule for the whole trip that gets you to your end point at the right time. Again, you don't need to stick to the schedule, but you can use it as a gauge as to whether you are ahead or behind schedule and whether you can slow down or might need to speed up.
Most of the fun of a tour is the freedom to make each decision as it comes and not worry to much about tomorrow.
Oh, by the way, and this is important: take a test trips of a couple of days to a week to see how it plays out for you. Even overnighters on a weekend are useful experience. This will help ease your anxiety and give you confidence.