Q: Deleting data from old ipad

No, you'll be fine if you follow the directions in the knowledge base article that led you here. You will be restoring your new iPad from the backup, not directly from the old iPad.

To emphasize...

Import all your files (photos, music, etc) and sync with your computer. Then, you should backup your old iPad via iTunes, as an encrypted file and/or backup to iCloud. If you already have the new iPad, set it up and restore it from that backup, then check if everything migrated properly. If you need to sell or trade in the old one first, before getting the new one, you'll have two seperate backups to use, so there's little chance of both failing.