Insulation, Radiant and Vapor Barriers - garage insulation question

I want to insulate my detached garage (both walls and ceiling). I am thinking of putting a ladder with storage in the attic which would consist of putting plywood down in the center to walk on. I am also considering using blow in cellulose insulation to save money. Only question I have is how do I insulate under the plywood I put down in the rafters between the sheet rock and plywood (2x4 rafters)? Should I just use an unfaced lower R-rated 3 1/2" batt, or could I use a rigid foam board insulation with higher R-value?

Thanks

Why not blow the cellulose in the garage attic first and then put down the plywood to walk on?

To begin, I am not much of a construction guy.....so this could be a dumb question: How would I blow the insulation in before putting up the ceiling sheet rock?

Blowing the insulated between the sheetrock and plywood will be a pain. You will have to make a couple of holes in each bay in the sheetrock in order to blow it correctly. Unless you are using ParPAC plastic, then its probably going to be a big pain in the butt to do. ParPAC plastic is a poly plastic that has nylon coord running through it like chicken wire. This makes it very strong and won't bow too much. If you blow it that way, you can put the sheetrock on after(of course doing the plywood before you blow it). That will also give you a vapor barrier.

Id put up a 4 mil poly on the raftersas a V/B then the drywall. Blow the cellulose in. Later clean it some where I want to put the plywoood down. a R 13 insulation in the walls paper to the inside of the garage