There's really no wrong way to do it, as long as you put enough effort into getting the goodies. It's good to find what works for you.
I have read that heat will not destroy everything, it does degrade some of the goodies. Mescaline is not the only enjoyable alkaloid in the cactus, so use the core! Mew (who used to be one of the resident cactus experts) said that about 30% of the alkaloids are in the white core. I'd have to agree with my experience.
My recipe is this:
I do blend (it's messy, but I think it makes it easier to access the alkaloids due to increased surface area in contact with the water). With each blend I add about enough water to fill in the gaps of the cactus.
I don't use acid, but if you use distilled water, as you always should when reducing a brew, it already will have a bit of an acidic pH.
I do three runs with my crock pot, each for a few hours. They often don't quite boil, or just barely boil. There's really going to be no difference in the time it takes between boiling and say 80 degrees C.
After each simmer I filter out the pulp.
I taste the pulp to make sure it is not bitter, and when all of the good stuff is gone it really has no flavor at all. Trust me, you'll know if there's alkaloids. It takes my tongue about 15 seconds to actually register, but man is it bitter!
For the final filtering I use a cotton cloth, which gets out mostly all of the small pulp particles.
Then I reduce. I actually like evapping down to a resin and gel capping, so I use a wide tray and a fan set up to reduce, so as to keep the heat off as much as I can. The crock pot is an invaluable tool for doing the cactus. It's great for the simmering stage and it's great for reducing. It applies a nice even heat that will not scorch and on low it will just get to boiling.
If you're planning on drinking tea, get it down to a practical volume. I rushed it and thought I would consume about a liter of fluid. I hit a wall where I could no longer drink the stuff, thus decreasing the intensity of the trip. Also, it took forever to drink, so the peak of the experience was not as well defined.
It's honestly one of the most horrifyingly bad tasting things I have consumed, only beaten by my first MHRB tea, where I skipped the decanting step.
Be an adult only when necessary.