@nawrp11 That's right, the section banks don't include CARS (only chem/phys, bio/biochem, and psych/sociology). It's not a big deal though, because CARS isn't nearly as different from the "old MCAT" as the sciences are. Apart from the timing changes (like getting 90 min for 9 passages instead of 60 min for 7), all AAMC CARS is good practice.
As far as
when to use AAMC materials, I'm personally a fan of spreading them out. It can be jarring to practice with non-AAMC resources for an extended period of time, then switch to AAMC passages. The only problem is that the Qpacks and section banks aren't sorted in terms of subject, so it's hard to (for example) sit down and do three acid-base passages after covering acids and bases. My advice is to start incorporating AAMC passages, in small chunks, as soon as you've at least covered
most of the science content.