It should not be a problem by backing up iphone to iTunes if there is no WiFi, as you can use lightning cable to connect iphone to PC or Mac.
Just to remind you that the Backup does not back up your personal files such as your music/videos files. You may need to sync them back into your iphone after restoration is completed.
Just another reminder, because of the latest iTunes version, the backup does not include your Apps files anymore (except those built-in Apps by Apple). It only backups those Apps pointers and tie them under your Apple ID.
So this is what i found out when i completed my restoration, the personal Apps were being downloaded one by one from Apps Store over the WiFi, after i signed in my Apple ID.
Yeah, WiFi comes in here. As WiFi will save me from paying 3G/4G network to download the Apps.
I hope this info may help you. and not confusing you 🙂