Much of your excitement will be realizing how actually undaunting it is. I agree that a short overnight trip is really helpful to sort out how you organize your stuff. But it's pretty simple, just get on your bike and go! And if you forget something, that's OK. It's the imperfections that make it fun--you can always buy something along the way. Feel like you need another t-shirt? Buy one in some small town. Need water? Go into a cafe and ask to fill up your bottles and get lunch while you're there. Raining hard? Stay a little while longer in the small town and explore. The friends who have had the least positive experiences bike touring are ones who have set unrealistic expectations for themselves, usually in terms of travel distance and time. Like trying to go 1,000 miles in 8 days with bad weather. As long as you have time, you'll make it and it will be beautiful.
My most helpful article that I would suggest is a handlebar bag, one with a clear front to display a map through. I pack all my clothes, food, and bike stuff in the panniers and then keep my map, wallet, iPhone, chapstick, Cliff bar, etc. in the handlebar bag. It's easy to detach, so anytime I want to go into a store, I don't need to dig anything out, just rip the velcro straps and take the bag in with me.