If you don't mind my throwing in a couple of cents, I would say you have a great starter system... and for a first grow, very very good.
Your seedlings came up strong and they developed nicely, but their overall vigor and branching topped out early because the setup you have can only take them that far. You didn't do anything wrong, but if you scale up here and there, you will get much bigger plants and yield next go round.
Be merciless with the oxygen, use a larger bin and switch to a simple sprayer system instead of that drip thingy. Increase the amount of water in your res, and keep it cool. Invest in a chiller, but if you don't have the money, do what I used to do and throw frozen water bottles in there... Get a bigger pump, hook some fans up to your light, and you will have more bud.