I also have a nexus 5, and I've gone through this. Here's my story...
The two apps I use for this sort of stuff:
ROM Toolbox is definitely the more versatile program and the one to get if you're only going to get one. It can do everything Titanium does basically, and much more. However, Titanium is sometimes preferred in specific situations.
ROM Toolbox can backup your apps, app data, system apps, etc. So can Titanium. But Titanium can keep multiple copies of backups, which is really the only thing it does better. When I'm restoring just a single app, I go to titanium (no good reason).
Now, all this aside, it's easy to screw up an intended backup/restore procedure when you are installing a new ROM or something. Things don't restore the way you expect, settings are gone, etc. And it's not always easy to figure out why. So here comes...
Nandroid, is like a noun/verb (very confusing) that basically means an image of your phone. You can only do a Nandroid outside of the OS (like in twrp or cwm). THis is definitely my preferred restoring method. When I restore my system (all apps, settings, anything) using a Nandroid, everything restores perfectly. If I try to restore within android using titanium or ROM toolbox doesn't work nearly as well.
So how do you make a nandroid? From ROM toolbox, you backup your ROM. It will reboot and do it automatically.
Hope that helps.