1.) Heres the big thing about the note 3.
You cannot revert (odin flash) back to previous builds of the note 3, it will soft-brick (maybe even hard-brick) your phone.
Meaning if you are on NC5 its not a good idea to dowgrade back to NAB. This is a smaller jump but ive read of issues. Though NEVER try to odin from kit-kat to Mj4 jellybean. They have different incompatible bootloaders, and it will brick. So ya no downgrading.. Unless you really feel comfortable with "engineering boot loaders" But currently the newest build is "NC5"
2.) think the most convenient root method is to..
-put chainfire's UPDATE-SuperSU-v1.94.zip onto sd card
-odin twrp 2.7.01.tar, (found in original development) or link
-immediately boot into twrp (Home+Power+Volume Up) and flash UPDATE-SuperSU-v1.94.zip
Now rooted with twrp recovery to flash new roms
3. Just another warning. Factory reseting with STOCK recovery for this device wipes internal sd card.
Edit/Add on: About knox: Dont worry too much about it. Once your rooted on stock rom, it will probably prompt to attempt to disable knox. just hit okay and thats probably the last you hear about knox. When you flash a new rom the rom devs have it disabled so it never prompts. But ya knox isnt really much of anything but a counter in download mode. Yes it cant be reset, but thats about the only thing that cant. You can still be fully unrooted, with official status. You probably wont have any problems with sprint. Theyd have to check download mode for the 0x1, and they would have to know what that means too lol. And you definitely wont have problems if you have sprint warranty.
Hope that helps good luck, I love this phone!