Dude i think everything looks good.... your putting too much thought into the whole grow thing.... let it go... its not ready for nutes yet your soil has them in it already..... chill off em and clip those lower leaves :) you'll be golden
Not bad .... yea 4 gallons is plenty of soil ... if its draining out the bottom... your good no chances of the roots running upwards... what kind of soil are you running again??
Dude my leaves were kinda yellow too at first but i just watered them no nutes and they just held up strong turned green again!! and nutes.... when your plant starts looking saggy and sad :(