Allen,
I actually think vinegar is Ok, maybe because I just use it with no observed ills and it's on grocery store shelves. Never heard of Ascorbic acid being used in horticulture, and am unsure of its properties.
Humic acids can work as chelating agents for micros and can remove some chlorine from tap water. That pH 13 on the MSDS sounds like a solubility issue, maybe the pH at which the product is fully soluble
I don't think they'd make a potent pH adjustor.
Look into Urea Sulfuric acid. The two substances alone can have some problems, but the combination is synergistic and safer to use. It is probably the better choice than phosphoric acid for hard water because of the tendency of calcium to precipitate with phosphates. Even with sulfuric acid, I can foresee some gypsum as a precipitate, but the calcium phosphates are probably worse for clogging. If you choose phosphoric acid, get the white food grade type, not that green stuff. Whatever of these two, you must account for the addition of extra nutrients into fertilizer calculations.
Regards,
Matt