Thanks for the quick replies!
I was a bit confused about 2) because I read somewhere that if you make a nandroid backup of a stock ROM, then install a custom ROM (non-Stock based ie CM, PA or OmniROM) you must flash the stock ROM again before you can restore the nandroid backup, or else restoring the nandroid backup will not work. Is this true?
Consider the following example, say I:
-flash TWRP on my device and root
-make nandroid of stock, rooted ROM
-wipe /data, /system, /sdcard and caches and reboot back into recovery
-ADB push a non-stock custom ROM .zip file and flash the custom ROM
-decide I want to return to stock, rooted ROM after a while
-Boot into TWRP, then wipe /data, /system, /sdcard and caches and reboot back into recovery
-ADB push my original stock, rooted nandroid backup to /sdcard while in reocvery
-restore nandroid backup
What would be the outcome of the above example? I'm very curious...but I'd like some advice before attempting something like this myself as I'm still kinda new to all this
BTW I'm now comfortable flashing back to stock using fastboot and the google facotry image to restore a Nexus device so I now know how to do this in case things go south. I'm just curious if this would work on a device where returning to a full stock state isn't so easy.