You could install Xposed Installer and look through the list of modules at
Module overview | Xposed Module Repository to see which ones you'd like. (Wanam is just about mandatory for everyone.)
You can also look for a list of bloat you can remove, to free up some storage. (Don't assume that, because you're never going to use an app, you can uninstall it. Some other app may call one of its components. For instance, freezing or uninstalling the Samsung updater could cause a problem with any of the Samsung apps if, for any reason, one of them will no longer run without the current update [as sometimes happens when the Android version is updated].)
Helium backs up your apps and data. If you're not rooted, the phone has to be connected to a computer running a little auxiliary program. With root, it runs by itself.
Look on Youtube or Google for Android rooted apps and you'll find tons of apps people consider must-haves for rooted phones.
Everyone is different. If you're a photographer, apps that a developer can't live without are just space-wasters for you, and having 5 different cameras and 4 different picture editors is a waste for him, but you'd feel lost without them. No one can really tell you which apps are best for you, but reading the articles and watching the videos lets you know what's out there, so you can make your own choices (which is what Android is really all about).