Tracking changed files/configurations in Linux

I have a small microserver at home that's several years old (HP Proliant Gen8, Intel Celeron G1610T). I installed Ubuntu 14.04 on it, set up RAID on 2 large disks with mdadm, and since then I've used it on and off for trivial things over the years. I've never paid much attention to it (it's still on 14.04..) but now I'd like to give it some love. I'm aiming to wipe Ubuntu and start fresh, but first I need to back things up. Is there a smart way to discern configurations I've added, changed, etc across the filesystem, so that I can back them up? If not now, what options are available if I were to start from scratch with this capability in mind? I will most likely copy /root, /etc, /home and select items in /var across to my RAID/NAS disks just for future reference back I am still curious what options are available. Thank you.