Couple things for you. Why do you run 12 gauge wire on a prewire for house wide speakers? 14 gauge is plenty depending on the distance. If you’ve pre sold the exact speakers before the prewire, that’s fine to use those brackets, but there are other brackets that do a great job as place holders for in ceiling speakers. Why do you not run Cat6 to the volume control as well? What about better control with a keypad or a touch panel. Sorry, never have been a fan of volume controls. Zero control except volume and an ugly knob on the wall. Are you putting in high end speakers and amps to warrant the 12 gauge wire? Just a few thoughts.

Spend the money on your speaker cables. Blue Jeans is the best value proposition. Most people don't have speakers that really need the perfection of Kimber cables.

It is a widly accepted practice backed by electrical engineering concepts to use 16-4 high strand copper wire for general purpose room speakers up to an eighty foot run distance. Then after 80, change to 14-2. 12-2 or 12-4 is a waste since the benefit at the low current is miniscule. If you have a high powered speaker running at 200-400W, then you should upgrade the speaker wire to a lower gage yet this is typically reserved for Home Theaters and media/listening rooms.

Any links to where to get the pre-install brackets? How universal are they?

Still never seen a video with Jose actually doing any work. Talk more than Zac.

Don't drill through center of joists.