yeah just put them in a 3 gallon, it doesn't matter. Yes nutes=nutrients, get something for tomatoes, ask around at a homedepot, or if you have a hydrostore go there. I wouldn't start with northern lights, if you want something really easy try something autoflowering. But just get seeds of a strain you will like. You should probably just by normal, or try bagseed for first grow, unless you have the money to spend.