Wow! I can't imagine planning that far ahead. Even for a coast to coast trip a few weeks is the norm for me. I did plan 5 months ahead for the Sierra Cascades trip, but that was because I had to wait until then for logistical reasons, not because I wanted to plan for that long.

Two concerns to consider:

1. Having a destination of something like a graduation means a firm deadline. Firm deadlines can be joy killers in my experience. YMMV though. Still, maybe consider driving to the graduation and riding home.
2. The country you are choosing isn't the most scenic or appealing for touring. But then that is my opinion and your opinion may be entirely different. I have ridden across Kansas twice, but it was part of a tour that also was in the mountains too, in both cases. Maybe you could consider riding through New Mexico. It is very nice, but would make the route longer. BTW, Oklahoma is my least favorite state to ride in so far. The roads are generally in poor shape and the scenery monotonous.