Great information, salsalady!
I did not see one question answered in that post -- do I need to be concerned about the pH level if I consume all the salsa I make within 1-2 weeks, and it is refrigerated when not on the table? You recommend a pH of 4.0, and this is needed under what circumstances?
(This isn't a dumb question, by the way!)
I'm not sure there's anything else to add! All good advice (from more experienced people than myself), but to summarize everything said in my own words to make sure everything is clear:
1. Vinegar isn't necessary, but if your pH is >4.0, you will probably want to fridge it to ensure safety. If you boil the sauce before you bottle it (in a likewise boiled bottle) it will also last for quite some time. <4.0 is "shelf-stable," meaning it doesn't need to be refrigerated, though most prefer to kick the pH down even lower for safety. (i.e. Vinegar is a good preservative)
2. Adjust vinegar-water levels for personal taste.
3. Hot sauce making isn't so much a science as an art... in regards to ingredients. There's lots of science behind it, but what you use is often up to personal choice. So long as you follow a few hard rules (Boil your containers, either keep pH down or keep it refrigerated, preferably both if you can, cooking helps but can adjust flavor).
One other thing to experiment with:
Different kinds of vinegar. A lot of your recipes, particularly habanero recipes, tend to tell you to use ACV (Apple Cider Vinegar). ACV imparts a lot of its own flavor. White wine or red wine vinegar imparts less, but also do tend to make it very sweet, though less "vinegary." White distilled vinegar is more flat "vinegar" with less another flavor. I personally use White House White Distilled Vinegar. It's milder than other white distilled vinegar and doesn't risk masking the flavor of the sauce itself.
Testing out a few different kinds of vinegar - even different brands of the same vinegar - may allow you to use more vinegar to improve the pH for safety without compromising the taste you want. If you don't have a lot of the peppers to work with, do what you know works. I'm not currently working with any harder-to-get peppers, so I have little to worry about - I'm just using store-bought jalapenos, serranos, and habaneros, so I can make a lot cheaper and can afford to lose entire batches without much worry. They're good to experiment with.
This being said, this reminds me that I probably need to lower the vinegar in my recipes...