Try type code *#0228# ?

what is your firmware version ?
if is latest no need to care about it at all

yes
no idea flash to older LL, if you want better wipe it 1st
for twrp, either you want to root 1st or flash twrp 1st also can, up to you
but I prefer root 1st then only flash twrp

nowadays all custom rom are either ported rom like note 7 / s7
don't even have any custom rom based on stock rom

same here, but right now I use stock rom without root at all due to want to play pokemon go

care to share which custom stock rom u are using ?

i guess the close to stock rom is this,.. but it is not xme,. http://forum.xda-developers.com/note-4/dev...-stock-t3440787

using latest miui 8 beta by wonitor. so far so good other than few bug.

Really happy with my note 4 so far even in stock rom and root it to make some tweaks. Save my money on extended warranty so I plan to buy my 3rd spare battery. How much the price on Samsung official store?

Yeah. Im agree cause I'm not really confident with rm70+ battery quality and usually on that price, the 'original battery' does not come with NFC.

Talking about NFC, anyone here using Samsung pay/ Maybank pay anywhere? 7eleven? I love to test it. With a proud and arrogant face at the counter lol

Never have problem with my note 4 signal. I had redmi 2  before, i think both receiption almost the same. Try to lock ur 4G signal if ur area 4g not really strong. 
From the phone dialer, dial *#2263# and the smartphone will bring you into the “Service Mode” select lte band part 1 and then select lte all. The downside u cant receive/make any phone call when u lock ur phone in 4G mode only.