And on the plywood, go buy a 4x8 foot sheet and cut it into 4 4x2 foot sheets. These are easy to carry into your attic one or two at a time and you can lay them down as “tiles” that span 4 16in joists. Easy to just lay them down (screwed to the joists) to where you need to get and also continue extending your tiles later if you want to either get further or complete your “floor” for storage purposes. And you can still take up one tile at a time if you need to get access to something like the top side of a ceiling light fixture.