You know what bro, Ive had so many variations on auto flowers, Ive had some that turned into 2 foot plants, and other that turned into one fat solid bud that only ended up being a foot high...so scrogging might not be for you. If i were you id just run it how they are, autos are already designed to stay short and bushy so scrogging is a little unneeded. As for the soil, 3 gallons is plenty and yes you should use molasses during the whole cycle. I usually use around a tablespoon the first few weeks (the beneficials in the soil love it, its like steroids to them) then after oh...the third week FLUSH THE FUCK OUT OF IT!!! Then continue as normal but with 2 tablespoons of molasses. I would stop using it 4 days before harvest, i know it pumps up your buds like big stripper tits but it will make them taste like Iron. also whats your light hood setup? is it one of those 400 completes that are all in one hood or is it a ballast and hood separate?