[Sprint  Galaxy Note 4 Q&A, Help & Troubleshooting] samep:
The thread and video are dated. A few key elementary facts are still relevant but as a whole, just not up to date. I wouldn't trust it and it lends to repeated help threads in this forum. If one read the OPs and threads of current ROMs in development and recent help threads, maybe less questions and help would be needed.

He omits current ROMs, didn't mention where the reactivation lock is for TW Android ROMs: Settings/Security/Reactivation lock (should be disabled). He doesn't mention Chainfire Auto root for Note 4 has been updated for 5.1 and will be key again for marshmallow (but that's only needed for rooting stock Odex). He also didn't tell you how to get to those old ROMs on his site. Some think you just Odin an old update but not so. That requires a 5.1 kernel matched with current bootloader rather than Odin downgrade.

The bootloader, while not locked to block root, is considered unlocked but actually is now security locked to block older security stock tars with lower security bootloaders. It's actually unknown until confirmed what tar you can downgrade to. It won't be KitKat or OB7 and some just after that. From OK1 update, I'm only aware that you can downgrade from OK1 to OJ6 and if you flash the MM leaked tar, you can still downgrade to OK1.

Kernels should be kept in zip form because backing up a kernel in TWRP doesn't backup /system/lib/modules to restore and some custom kernels modify or add modules which may not work restored boot.img And restoring stock kernel on a rooted phone would cause a boot loop. So to restore that, you'd need to full un-root in SuperSU to avoid the boot loop there as well as restore the stock /system/lib/modules.

Root methods: unless you're using the full un-root or wiping everything but extSdCard (particularly user data and internal memory), you don't fully remove systemless root. Flashing a ROM or SuperSU with system based SuperSU over systemless root without the wipes would break things like root. Not seeing the SuperSU app or loss of ability to add new apps to superuser would be impacted but also a boot loop is possible if but patching stock kernel su.img to boot.

The basic principal is that to flash the custom deodexed ROM you need for Xposed, just make sure you're on the right update, Odin TWRP and follow the OP closely. If wiping internal memory is suggested by OP, I'd suggest that. To keep things simple, I backup and wipe everything but extSdCard for ports or where Xposed or systemless SuperSU is used. I typically do the same for stock tar updates as well.

As to recommended ROMs, I'd suggest any deodexed OK1 ROM for Xposed. tx_dbs_tx has a variety of OK1 ROMs. Freeza has one with Xposed integrated with Xposed modules in system. If Note 5 Moar port is a good fit, I'd recommend trying without Xposed until you determine the minimum of Xposed mods you're lacking so you're not overlapping features and you're getting to know the stability of it, first.

Rooting a friend's phone? IMO, you should be very sure and confident before proceeding and advise rather than do all the work and take the risks yourself. Use the correct USB driver, not just one that works. Setup his computer to root and sustain that phone.