Unless I missed something, this is a Verizon Note 3, which means that they nailed the bootloader shut, then welded the nails. You can't flash a kernel.
Put a ROM zip file on the SD card, boot into Safestrap, create a slot, install the zip file, back up the ROM if you want, boot the system and you're running the new ROM in slot 1. If you don't like it you can boot back to Safestrap, wipe slot 1, make the default slot the active one and boot back into the stock ROM.
Make a backup of the stock ROM and keep it on the SD card and on your computer (and on the cloud if you really want to be safe).
If you totally screw up - like installing a keyboard to the only slot you have (a keyboard won't boot, ask me how I know) - you can still boot to Safestrap, restore the stock ROM, or any other backup, and you're good.
I ALWAYS make a backup of the current active ROM before making any changes. Then, if I really mess it up, or it bootloops, or some other nonsense, I boot to Safestrap, restore a good ROM, and I've wasted 5 minutes, not ruined a phone.
I guess TWRP alone is okay, but 5 slots is nice to have. (My solitaire game runs too fast in my normal ROM, can't actually see the hints, but I have a ROM that's so slow it's painful - but it's perfect for the solitaire game. Easy to switch between them.)