Here is how i understand it:
Sweep- You get your private keys from your wallet which can allow you to re-use an address. Sweeping also makes it possible to have multiple private keys
Correct.
Wrong.
Import simply copies the private key to your wallet. Sweep sends the bitcoins to a new address in the wallet instead.
Sweeping is generally safer but the bitcoins are not instantly available. Simply importing the key into your wallet has a weakness that you must take care to avoid. The old wallet could be compromised and the bitcoins could be stolen. For example, if you are importing from an unencrypted paper wallet, the private key is still available to anyone that obtains the paper wallet. You must ensure that the paper wallet is completely destroyed after importing.
Partially correct, everything except for the first sentence. Sweeping basically means sending all of the bitcoins in the previous address (using its private key) to another existing or newly created address in your wallet.
