Alot of trouble for access, insulation would be my first concern,
storage or access the least of my worries. It is unheated, right. To get
access you would have to raise the floor up very high. Im my case 18".
Insulation codes are only minimums, optimal amounts would be found at
Energy Star, even manufacturers recomendations I would follow with ever
increasing utilities. The attic is the cheapest and easiest place to
make the greatest difference in utility reduction since heat rises and
it is cheap to do. Optimal ratings are often double of code.