I will work backwards.
You can backup with iCloud and iTunes. I use both. It will not affect your iTunes backup at all if you backup with iCloud. In fact it's a good idea to have both backups. However, this has nothing to do with texting on the iPad.
You have to set up messages on each device. You don't do this in iCloud. On your iPad - Go to Settings>Messages and turn Messages on in the settings. Sign into your Apple ID. Your email address should be verified. You should then get the option to use your iPhone number as the contact. Go to Send and Receive at>You can be reached by iMessages at and select the phone number.
If the phone number does not appear in that setting, you may have to sign out of Messages on the phone and the iPad and then start all over again.
This might be helpful. See the section at the very end of the kb article.
Also note that you can only message with other iOS users that have messages already set up on ther devices. You cannot message with Android users.
Using FaceTime http://support.apple.com/kb/ht4319
Troubleshooting FaceTime http://support.apple.com/kb/TS3367
The Complete Guide to FaceTime + iMessage: Setup, Use, and Troubleshooting
Troubleshooting FaceTime and iMessage activation
iOS: FaceTime is 'Unable to verify email because it is in use'
Using FaceTime and iMessage behind a firewall
iOS: About Messages
Set up iMessage
iOS 6 and OS X Mountain Lion: Link your phone number and Apple ID for use with FaceTime and iMessage
How to Set Up & Use iMessage on iPhone, iPad, & iPod touch with iOS
Troubleshooting iMessage Issues: Some Useful Tips You Should Try
Setting Up Multiple iOS Devices for iMessage and Facetime
FaceTime and iMessage not accepting Apple ID password
Unable to use FaceTime and iMessage with my apple ID
FaceTime, Game Center, Messages: Troubleshooting sign in issues
How to Block Someone on FaceTime
My Facetime Doesn't Ring
To send messages to non-Apple devices, check out the TextFree app https://itunes.apple.com/us/app/text-free-textfree-sms-real/id399355755?mt=8
How to Send SMS from iPad
You can check the status of the FaceTime/iMessage servers at this link.