A few thoughts:
50 ppm borate is fine in my opinion.

A cheaper source of borax is 20 mule team borax from the grocery. It's the same stuff except that it is the decahydraate form (it has 10 water molecules attached instead of 5) so you need a bit more by weight for the same borate level (60 oz by weight will raise 1000 gallons 50 ppm and needs abut 30 fluid oz of muriatic acid to keep the pH in line. The pentahydrate form requires about 45 oz by weight and the amount of acid to achieve 50 ppm rise in borate in 1000 gallons while using boric acid requres about 38 oz by wieght and will very slightly lower the pH but this is not a concern since it will rise on it's own as CO2 outgasses.)

If you want a pH neutral borate souce that is available commercially then Proteam Supreme Plus is the product you want. Proteam Supreme is exactly the same at Bioguard Optimzer (sodium tetraborate pentahydrate). The Supreme Plus is a mix of boric and and the pentahydrate form of borax to make it pH neutral. However, all the commercial forms of borax are MUCH more expensive than 20 mule team borax from the grocery store.

The main reason to use sodium hypochlorite (particularly since you have a vinyl liner) is that calcium hypochlorite is slow dissolving and can bleach the liner if it falls on it undissolved. Also, Sodium hypochlorite is what the salt cell is is actually making. As far as worrying about the 'freshness of the bleach" it's really a moot point. Unless you are buying it at a discount store or dollar store it's probably fresh. Walmart has a big turnover so it's a good place to buy it. If they sell pool chlorine in refillable carboys in your area that is often the best deal. Just buy enough for shocking and don't stockpile it so it does not stick around for more than a month or two before getting refilled. One gallon of 12.5% pool chlorine will raise you pool about 6 ppm, btw, so a 2 1/2 gallon carboy should be just about right for shocking your 22000 gal pool (or 5 gallons of 6% laundry bleach). If you use cal hypo predissolve it first. You do not want undissolved cal hypo going through the salt cell or falling on your liner.

As far as your metal problem, Were the stains brown (iron)? Do you fill with well water? What kind of salt do you use? I have seen some fine crystal "pool salts" that have caused iron staining which is why I recommend using solar water softener salt (The larger crystals do not need anti caking agents). I suspect that anti caking agents are sometimes added to the fine crystal pool salt or they are using food salt (which also contains anti caking agents) and repackaging it. Yellow prussiate of soda (sodium ferrocynaide, an iron salt) is used as an anti caking agent in food salt.