Bunch of questions about my new Mac

I would recommend against installing a version of OS X older than what shipped on the Mac. Apple often ships minor revisions to the OS specific to the computer. For example. I might have a Mac that came out in 2011 running 10.8.2 (and I've upgraded from 10.7) but your brand new Mac that came out last week ships with 10.8.2 with a slightly different build. My Mac could be downgraded back to 10.7 as that's what it shipped with, but yours could not as specific tweaks, drivers, etc would be built absent from prior versions.