Yes the rom has to be based on NC5, just like the X-Note, you might get an NAB based rom to work. But, you can't go back to mj4 or older you will soft brick your device.
You can flash any of the Note 3 Roms ,updates, mods and so on just read everything carefully! And do research on the roms you wanna flash. Read through all the posts if you need to know something. Most of the time its been asked before and the answers are out there. The xda search bar is a useful tool for such things and if you dnt find what you need just ask around. Theres alot of good kind people here that will help.
Yes, but before you do check this out http://forum.xda-developers.com/note-3-sprint/help/4-4-4-download-mode-t2877528 and this http://forum.xda-developers.com/note-3-sprint/help/upgrade-to-4-4-4-revert-to-4-4-2-t2878402 good luck !!
