Default [Q] Galaxy Note 3 sm-n900x (demo edition)

I am total newbie to android. I was an apple user for many years.

I bought a demo edition of galaxy note 3. A friend of mine who is an expert app developer replaced the demo firmware to a working firmware.
This phone will boot loop if a normal firmware is installed because of missing modem.
Now I want to do three things.

1) Backup my whole current firmware and all the drivers without rooting. This is very important to me. ( I do NOT need to back up apps, photos, etc etc)
2) Root the phone (for using adhoc wifi and few other stuffs). I cannot find any files and instructions for rooting this partcular model ( sm-n900x).
3) Install a custom firmware

I want to backup the firmware before rooting in case anything goes wrong.
Please tell me if it will be possible to do these three things and how.

Another question..... does rooting replace the full firmware/ part of the firmware/or any drivers??