When I go in I cloud data storage, it says I have 3.3gb from an old phone which was replaced by a new phone. The new phone has 1.2gb of data. Can I now get rid of the data on the old phone from the i cloud.

This is the backup of your old phone but you can't see the contents of the backup. You can go to Settings>iCloud>Storage & Backup>Manage Storage, then tap the name of your old phone under Backups. This will give you some information about what categores of data are included in the backup but you won't be able to see the actual data. To delete the backup, scroll to the bottom and tap Delete Backup. This will free up the space it is taking in your iCloud account.

When you delete an iCloud backup it is permanently deleted and not available in the future to restore from. The backup of your second phone only contains the data and settings from that phone. If any of this data was inherited from your first phone, it would be contained in the backup of your second phone as it was on your second phone when it was backed up.

If you want to keep backups of your old phone, back them up in iTunes and they will remain on your computer. Even if you are backing up to iCloud, you can manually back up your phone in iTunes by right-clicking on the name of your phone on the left side of iTunes and selecting Back Up. iTunes will see each device as a separate device, and will maintain the backups separately. Do this with your first phone and you can then delete the iCloud backup and you will have the iTunes backup on your computer should you ever want to access it.

Can't really say. You would think they would be close, especially if you had the same camera roll photos and videos, which are often the largest item in your backup.