Hello, I plan to add flooring for seasonal storage to my attic(house was built in 51).

How should I determine if the joists need to be reinforced to accommodate flooring?

I plan on using 5/8 OSB. Is that sufficient?

Also, there's blown insulation that's flush with the joist. Will I cause problems going right over it, or should I make a space between the floor and the joist by furring it up?

Any help would be appreciated.