@DaltonLurnurWith the shield master feat and extra attacks as a fighter, can i attack, shield master shove, attack? Yes.
— Jeremy Crawford (@JeremyECrawford) July 21, 2016
@DaltonLurnurWith the shield master feat and extra attacks as a fighter, can i attack, shield master shove, attack? Yes.
— Jeremy Crawford (@JeremyECrawford) July 21, 2016
You can announce that you are taking the attack action, shove before any attacks and then use both your attacks. It doesn’t specify that it is after an attack.
No. Jeremy Crawford later changed the ruling in 2018 that you have to complete the attack action before the bonus action. His tweet can be found on the internet and it is a highly unpopular ruling.
Irrespective of Crawford’s later change of mind on Twitter or wherever there is nothing in the rules as written that says you can’t announce an Attack, then interrupt the Attack to take the Shield Master feat bonus action and then continue with the Attack action. There is also nothing in the rules as written about when you can interrupt the action, so from my perspective you can interrupt before you actually execute the mechanics of any attack, including the first. The only potential downside to this is that if the result of the bonus action leaves you with nothing to Attack (e.g. you shoved your opponent off a cliff) then you cannot change your action to do something else.
At the end of the day it is down to the DM to interpret the rules as written for their game. They can follow Crawford’s advice or not. It isn’t gospel until its in the rules, and even then DMs can always homebrew their own variants on that as well.