Main thing to worry about is time. Are you planning 100 miles a day because you want to get across the state as quickly as possible? When you start loading up your bike elevation and wind also become things to consider. The other thing to think about if you have never rode more than 50 miles in one bike trip is is your ass ready to be on a bike seat for that long? On flat terrain I could bike and bike all day if my ass didn't start being extremely painful after 40 miles. After time you get used to it and covering 60-80 miles will seem like a drop in the bucket.
If you don't do too much training before the ride I would suggest starting with a pace of 35-50 miles a day, after about a week of riding like that (give yourself at least one rest day every 4 days or so) you will find that if you want you can easily cover 50-60 miles a day, but might find yourself stopping to enjoy the scenery along the way (a dip in a lake/hotsprings, a hike through a state park).
The other reason I suggest not to restrict yourself in time (or at least give yourself ample time) is because you never know what you'll run into. You might spend an entire afternoon laying in a ditch under a tarp waiting for thunderstorms to roll by.
Training beforehand, I would say start easy, bike 10 miles a day 4 days a week. Add a mile or two to each ride each week (make sure and give yourself rest days). A few weeks before the trip do a 'shakedown' like eribrav suggested. Bike 50 miles to a state park or place you can camp, and then bike back the next day. You will find out what you need and do not need. You might feel like you need a bunch of changes of clothes, but really, you just need two sets of biking clothes (maybe three), and one set of clothes to wear off the bike. Get some biodegradable soap, and you'll be washing your clothes in gas station sinks and draping them off the back of your bike to dry.
Check
Adventure Cycling take a glance at their maps. They try to pick roads with less vehicle traffic, or large shoulders. You will likely come across other cyclists doing the same thing you are and it's always fun to ride with new people for a day or two.
Enjoy, long distance bike trips are a blast!