If you read carefully, you'll see "original" refers to the applicant's civil documents, not "everything".
1. No do not send the original. Scan and print
2. Only if things have changed and you need to update. Otherwise, a copy of new tax return if applicable (Not really applicable until April 15 but ok if you already filed it) and an updated pay stub.
3. If you are shown as living in the USA, yes, but really not needed.