I must admit, when I saw the title to this post, I got excited and thought hmm, maybe I’ll try that. But after reading all of this, that’s a hard no for me! Thanks for providing such good info!
If it interests you, and you are willing to let someone else do the hard work for you, I recommend you look into Justin Rhodes' make at home formula. It checks out well in a feed calculator, it compares favorably to off the shelf feeds, has enough "buffer" that a single below average feed ingredient won't make a disaster out of the balance, and it has the benefit of large scale use over time. (Except the fish meal - take away the fish meal, and the whole recipe falls apart - but as you learn about feeding birds, why the fish meal is THE KEY ingredient in J Rhodes' formula becomes obvious).
Can it be made at home without access to modern shipping and internet ordering? Nope.
Is it cheaper than buying off the shelf? Not for most people, in most circumstances.
So why do I recommend starting there??? Because like a home brew package that starts with pre-made malt syrup and hops pellets, its a way to get your toe wet that won't kill your flock. Once you have researched, and well understand, exactly why each ingredient in that formulation has been chosen, you can begin to research individual potential substitutions to take advantage of locally sourced ingredients which may be cheaper or more readily available.
...and knowing what I know, even though I maintain a flock of 50 - 100 birds at any given time, and its a 1 hour (round) trip to the closest feed store (I'm in a part of FL remote enough that the county building inspector asks that I send him photos from my cell phone, so he needn't visit), I don't make my own feed, nor do I attempt to grow my own feed.
oh, and whatever you do, stay away from Garden Betty and the cute Youtube teen who can't do algebra. You will see her adding percentages and proclaiming a protein content higher than any of her individual ingredients. Any idiot should understand how assinine that is, and yet she has thousands, if not tens of thousands, of devoted followers.