My plan would be to have four states for four regional previews. Then after that you have each region vote as a block two weeks apart.
So:
Last Tuesday in January: Iowa
1 week later, early February: New Hampshire
1 week later, mid February: South Carolina
1 week later, late February: Nevada
First Tuesday in March, Midwest votes as a block (From the Dakotas, Nebraska, and Kansas as far east as Ohio with Kentucky as the southern line)
Second Tuesday in March, "Northeast" goes, as far south as Virginia and West Virginia.
Third Tuesday, the "South," as in the ex-Confederacy plus Oklahoma and minus Virginia, also including Puerto Rico and Virgin Islands.
Last Tuesday in March is all the rest, the West and Pacific colonies.