check your strains are 100% auto, or your gonna end up with 8ft plants. a lot of auto strains are not 100% solid, and tend to need 12/12 before theyl bud, if your in the uk then they wont start budding until september, and youl be in danger of frost before they finish. so just do a bit of research onto the seeds first.
as long as theyre a perfect solid auto then youl; be ok, and could get 3 harvests in if you plant your first now. bewareof squirrels, they like to eat them, also snails and slugs are a pest. you wont need to water much, as it always rains, i suspect thats why your thinking of using ams??
veg nutes i wouldnt bother with, the sun has enough power. but id use a little big bud every other water for a couple of weeks in flower, also not really necessary outdoors, but you will see a diffrence.