You can't backup your iTunes library from your iPad. You can backup what is on the iPad with iCloud. But any non iTunes purchased content that you had in the iTunes library on the Mac cannot be backed up with iCloud. Only purchased content from the iStores, your camera roll, device settings, documents and data .... Are backed up with iCloud.
Continue to backup with iCloud until such time that you decide to get another computer and can use iTunes again - if you decide to do so.
How to backup and restore from a backup