[Note Edge Q&A, Help & Troubleshooting] jooniloh:
What you want to do is make a Nandroid backup in TWRP. With a nandroid backup, if anything goes wrong with anything on your system, 99% of the time, you can restore the backup and your system will revert to EXACTLY how it was when you made the backup (root, apps, settings, EVERYTHING).

What I suggest you do is get a Micro SD card (you need one large enough. The Nandroid will be as large as however much is on your phone (NOT including your internal SD card). Ergo, if you have a 64GB phone filled to 50GB of application data, you'll need something with around 60GB (50GB + system, modem, efs, cache, boot, etc.) of space for the backup.), put the backup on that, and move them to a safe location (like your computer, or an external drive). To make a Nandroid, boot into recovery again, press "Backup", make sure all the partitions are selected, make sure storage is set to "Micro SDcard", then swipe.

Once the backup is done, turn off the phone, take out the SD card, and put it into your computer. Keep a safe copy of your backup (it'll be in TWRP/BACKUPS/<8-digit hex ID>/<your backup name>) somewhere and do this regularly. I suggest you also give your backups detailed names so you remember when you made each one, or what you did right after making that backup (like if you made a backup before flashing a certain file that you don't know if it'll work correctly). That way, if you need to go back to a backup, you can figure out which one to go back to easily.

Once they're on your computer, I wouldn't keep the backups on your Micro SD card because they're large and take a lot of space. IF you had the 128GB Micro SD, maybe keep the latest backup for convenience, but that's about it. Keep the rest on your computer. You can delete backups from your Micro SD by going to "Restore" in TWRP, selecting the backup, then pressing "Delete Backup".

An important thing to keep in mind is that Nandroids do not back up your data on the Internal or External SD cards. You can access both these locations through your computer though so make backups of them manually. Otherwise, you risk loosing downloaded files, photos, etc.

For less serious things, you can make a backup of apps and their corresponding data in Titanium Backup. This wont save you from corrupt systems files or other more serious issues, but if you switch to a new ROM and want to take your apps and data with you, Titanium is your friend. Titanium WON'T back up anything else besides apps and data. If you need a more comprehensive guide on Titanium, give a shout, and I'll see what I can do.

As for backing up aboot. Yes. Definitely do that. I'm reading through the guide posted there now. If you need any clarification or help with the steps, don't hesitate to ask. When in doubt, just ask. Some of the tools used could do some serious damage to your phone with even a slight error. Also, it's always a good idea to read all the instructions through once before doing anything so nothing surprises you as you're doing it.

The closest thing to a factory reset you can do quickly is the "Wipe" option in TWRP. Otherwise, to truly factory reset, you have to flash a stock rom. This will unroot AND remove TWRP.

Will the 915V ROM work for the dev edition? This was brought up before but never confirmed or denied as I remember.