The jugs I buy (Walmart generic 8.25%) are 121 oz so roughly 0.95 gallons. In a 50K pool, each of these jugs will add 1.6ppm of chlorine.

If you find that you have only 30ppm of CYA, you'll want to bump it up. I'd go up to at least 50. It's awfully hard to keep chlorine in a pool on hot sunny days with a CYA of only 30. One of the gals who used to help moderate on this forum also lives in Louisiana. She deliberately kept her CYA around 80 I think (if I am remembering correctly) because otherwise she had trouble maintaining adequate chlorine levels. A plus of a higher CYA is that you don't have to dose as often with bleach.

Regarding your question about why Borax instead of baking soda --------- Borax will raise pH without affecting Alk much.

Good decision to buy the kit. You won't regret it!