Ok, all good questions. So you can't go wrong with good old GH. It's not the absolute best, but it is a good starter while you dial everything in.

Each nute manufacturer has either a mixing/ratio recipe or a calculator on their website. There are also directions on the bottle, but those vary a bit.

Now here is something that a lot of people don't understand about nutes: The amount you make should be based upon one feeding per week! Let me explain: If your plants drink 5 - 8 gallons a week, let's say 1 gallon per day, then you would mix 1 gallon of the nutes/water, and then just continue to feed water for the rest of the week. That's it, all the rest is waste.

You'll do great. BTW, post a follow up thread when you plant your seeds or cuttings because the recipe for that is different.