I too use FFOF and I don't use jack other then the soil from the bag. I use airpots though so they allow for draining easy like. What pots are you transplanting into? Are there plenty of holes for drainage?
Really, I don't think it would hurt if you used said rocks, to be safe.
if you can possibly get any bigger containers do so,i personaly like 5gal or above,it will help in the size of the plant no doubt,but yea should be good to go with that 1.
i take mine out all the time to check the root mass never seem to phase them in the slightest as long as you dump them into your hand and dont pull them out by the stalk.