Fair enough, but the thing is there IS an iTunes equivalent... Actually, a ton of them. Your phone is always backed up either in Samsung's S-Cloud or in Google's (and years before iCloud happened); of course, you have to enable it for this to work. If you own an Android, you should have created a Google account at some point, even if you don't use GMail.
Your apps, just like iTunes, are always 'saved' in Google Play. When you sign in to a different device with the same Google ID (same as with Apple ID), your phone will sync and will re-install all your downloaded apps and purchases (which is why I suggest you always do the phone's setup while on WiFi if you don't want to blow through your data allowance in a day).
Now, as for music and pictures and documents, you have Samsung's "iTunes", called Kies. Or you can use another software of your choice like MyBackup or the always popular Titanium Backup. These apps will let you transfer most of your phone's data over SD card or Dropbox sync. The advantage with these is that it also saves app data and preferences, but I find that's it's always smoother to just do a 'clean' install of every app in every new device (yes, even in Apple stuff). But that's up to you.