For experienced oat feeders only?

Okay, so I have been doing a lot of research on natural horse keeping. My horse is already barefoot, and pastured 24/7. I want to feed him more naturally, too. Long story short, I did my research and have decided to feed oats. I understand from reading a few sources that because oats do not have balanced amounts of calcium and phosphorous, that feeding small amounts of alfalfa can make up for it. I would feed alfalfa cubes, because baled alfalfa is pricey and hard to find in my area. So my question is, how much/many alfalfa cubes should I feed? For my horse's weight of about 950-1000 pounds, it is recommended to feed 3-4 pounds of oats a day, which equals to 3-4 quarts, or two standard feed scoops. There is one other boarder at my barn, and she is interested in natural feeding, too, and is relying on me to do the research. The owner is fine with anything we decide to do, because we kind of run the barn for him. I also heard feeding oats is cheaper then buying mixed feeds like pellets or sweet feed. How much do you pay for a bag of oats? Alfalfa cubes? Do you find it cheaper than buying sweet feed or pelleted feed? I personally hate sweet feed, so I am eager for a change. Also, if you have any other suggestions for additional supplements to add to our horses' diets, they will be appreciated. I heard black oil sunflower seeds, flax seeds, linseed, and chia seeds are beneficial. I also heard about vegetable oils and cod liver oil, apple cider vinegar, and wheat bran. One source said to provide free-choice oat straw for horses to munch on even though it has little nutritional value. Any experiences or opinions on feeding naturally are welcome, as long as you don't bash on me or my decisions. Thanks in advance.