Alaska May 1st, north or south first?

I think your timing is perfect. That is exactly what I did last year and everything was open prices had not raised yet (except the already robber baron prices in Canada for nearly everything)and there were no crowds...there were plenty of RVer's there none the less.

I would go to Skagway, Valdez, Seward and Homer First. These are astoundingly beautiful places that deserve plenty of time. Then head north. Also your chances of seeing Denali are greater in May than in June or later.