mobile

I have a pristine looking insurance replaced Note II that I'd like to Root and Rom with a stable Rom that retains T-Mobil's WiFi Calling feature.
Also, I'm getting the unlock code for the device sent to me by T-Mobile; which I'd like to do as well. I do have a T-Mobile SIM for it and can get at an AT&T SIM to unlock it if necessary.

As far as Root/Rom goes; I'm fairly certain this limits me to Android 4.3 and below; since T-Mo hung Note II users out to dry for a factory 4.4.x update; and I need the WiFi calling feature to work properly.
This specific device showed up with the following on it and is currently locked.

Firmware: 4.1.2
Baseband: T889UVBMD1
Kernel 3.0.31-935627
Build No: JZ05K.T889UVBMD1 (probably redundant info)

I have 2 Questions to start:
1. Should I unlock this before or after flashing root/ROM?
2. What Root/Rom(s) is (are) stable and let's the T-Mobile WiFi calling feature working properly. (I've seen Info on Jedi Rom, not sure which of them would be best or if there are others that keep WiFi Calling)

Some advice on this would be sincerely appreciated; since I have no experience with unlocking and/or root/ROMs; though I've been reading and really can't find info on my first question.

TIA to anyone that can point me in the right direction.

cef1000