They still go by watts, but a better way to tell how bright any fixture is is to look up their PAR value. PAR is just a fancy way to how how bright a light is through a certain amount of water or a certain distance away from a light. This is all probably sounding like way more complicated answers to your question but its not as hard as it sounds.
Plants need micro and macro nutrients which are just fertilizers. You can get liquid fertilizers like from Seachem, they work well and are easier but you will pay a TON more in the long run. Or you can get dry fert mixes from Green Leaf Aquariums for about $30 and it will last well over a year, you would need a digital scale that measures in grams though, this is also a whole lot easier than it sounds too. I have a picture of a spreadsheet that says how to mix the dry ferts and how much to dose per 10 gallons