to plan it and fly my plan.
Hmmm.... I have flown from Northern California to Missouri in February every year for about 5 years. There is no plan other than it changes hourly based upon weather. I have also done the route many other times going both ways.
I'm also pretty sure he's going to want to fly it low, like 1000 AGL.
Pretty low.....ha, other than power checks I can count the times on one hand that i have been above 600 AGL in the last 10 years. Bear in mind that you do not want to be high above the Rockies you will exceed MSL limits.
If it was me, you would not go above 500 AGL, and it has to do with comfort level.