I ve used both 7 gallon is better protects roots from heat better, less subject to nutrient sensitivity,bigger plants thats a lot of light for a room that size
air pumps and air stones are oldschool use powerheads, used in aquariums much more efficient at ciculating water. an airstone does not create much circulation.surface movement creats dissolved oxygen in water condenses water molecule which makes it work better check out thewaterbrewery.com
seed are much stronger, better yield and more potent. however seeds are for the purest they take a while to start and they have to be taken care of, not for money growers