Unfortunately, your bootloader is locked now, so trying to ODIN to 4.1.2 won't unlock it. There's not an easy way to unlock it now (search the threads and you'll see that Mobile Tech videos can downgrade for a price... and someone else reported that they used an "unbricker" method to downgrade... but others don't appear to have had as much success).
If you stay on 4.3 MJ9, you can still get root, run root apps/ Xposed, etc... And with 4.3 MJ9, you can also use Safestrap to run custom Touchwiz ROM's.
If you take the OTA to kit kat, there's not a root method currently for our Note 2's, so you'll be running pure stock.
It's totally up to you, but if you want root (at least for now), you'll want to stay with 4.3 MJ9.
Edit: You can check out Safestrap at this link: http://forum.xda-developers.com/show....php?t=2704992
Here's a link to the saferoot method for 4.3 MJ9: http://forum.xda-developers.com/show....php?t=2565758