IPhone – If you backup your iPhone using iTunes, is it a full backup even if on the iCloud settings it’s not

If you use iCloud Photo Library, then your photos won’t be uploaded to iCloud for backup. The same goes if you use iTunes Match and MUSIC: you music won’t need to be uploaded to iCloud for backup.

If you don’t use those services then yes, your iCloud backup will contain your photos and music. Otherwise you wouldn’t be able to restore your device the way it was.

And yet, even though I’m an iTunes Match and iCloud Photo Library user, my fairly barebones iPad takes up 1 GB of storage for backup.

My iPhone has a few more apps, (2 pages’ worth). However under iCloud → Storage, only one app stores over 200 MB (Runkeeper) with everything else taking under 50 MB. The vast majority takes up mere kilobytes. I don’t backup my Health data because this seems to be causing issues. Somehow my iPhone’s backup takes up 2.2 GB.

As far as data consumption, I believe iCloud performs differential backups, because while the initial backup takes a significant amount of time, subsequent backups seem to complete much more quickly.

Apple has a great article enumerating what gets backed up for each level of iOS.

• iTunes: About iOS backups

Pay close attention to the section titled iTunes will back up the following information and note that by setting a passcode, Apple backs up more of your device's keychain. Also this article covers using iTunes and iCloud to back up since each has strengths and weaknesses in terms of backing up an iOS device.

In terms of the things you enumerate - all are backed up except the one you didn't want (the OS itself and firmware for the device).

I would encourage you to also sync contacts (and other data) so you have a second backup (or even the ability to make a third backup of the synced data) since losing contacts is an event that is very painful to recover.