I almost never make hot sauce exactly as described here. This is a base template around which you can hang adjuncts, and almost every part of the recipe can be omited or changed to alter the character of your sauce.

Rationale:

Caramelized onions as a base is the first step to building depth of flavor in the sauce. 

Roasted Red Peppers provide sweetness and fruitiness that melds well with the flavors of the hotter peppers. You can substitute with Fire Roasted Tomatoes for a slightly different flavor profile. You can omit these for a 'purer' flavored hot sauce.

Building a satisfying burn requires a mix of peppers. I think of it like perfume, with a bass, middle and high note. The milder peppers (fresnos or whatever) provide the bass note, while the hotter peppers provide the middle and high notes.

If I'm using ultra-hots (reapers, ghosts, scorpions), I will generally add 4-6 (or sometimes more) to the base recipe. The heat will quickly dominate with more than 4 ultra-hots in play.

The vinegar/water/salt ratio here will give you a shelf-stable sauce that will last for several months in the fridge. You can increase the vinegar to create a sauce with a more acid-forward flavor profile. Do not omit or reduce the vinegar, as this will make your sauce susceptible to contamination.

When you taste your sauce after blending, if it still has some residual heat it will taste hotter than it will once cooled and in a bottle. I typically blend, then let the sauce sit in the fridge in a sealed container for a couple of days before making any final adjustments.

If your sauce is hotter than you would like, you can modulate with sugar (I keep a supply of Simple Syrup in my fridge for this).

This sauce will separate if left to stand, but a quick shake will recombine. To prevent this, add 1/4 tsp Xanthan Gum to the sauce after blending, then pulse the blender a couple of times to evenly distribute.