After you file

Yes...you must wait for that too.

 

You cannot amend until the middle of Feb anyhow  (OK, it's really 6 Feb)

….but you really need to wait until the end of FEb to amend, so that you KNOW you have everything possible that you need to amend....you don't want to have to amend 2 times

____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*