If you are going to ferment the mash, there is no need to cook it. The reason you ferment is to keep it shelf stable and bring the pH below a certain level. Choose one or the other, not both. If you are going to ferment, let it go for no less than a month. The longer the better, but trust me I know how impatient one can get waiting for a sauce to finish. Never open the container. Keep it sealed with an airlock of some type. Once you open it, you let out the CO2 keeping mold from forming on the top of your mash.
Also, I am not sure about leaving any part of the stems on. If you blend it up too much, you'll end up with bits and pieces of the stem in your finished sauce. Never use a blender that will break up or damage the seeds either. You are only trying to break up the fruit part of the pepper.
Personally, I use 6% of salt for Habaneros, and around 8-10% for milder peppers like Serranos or Fresnos. Play with the amounts, but if you use too little it will mold and become unusable. Do not add garlic, carrots, etc unless you specifically want those flavors in your sauce. You can always add that kind of stuff to your pepper mash later if you want.