When a player receives a blackjack, does the dealer automatically pay it off once the initial player cards are dealt or does he just start at first base and then pay it off when he arrives at the player BJ?

Once the dealer pays the BJ, does he immediately collect those 2 cards or does he wait until the end of the round and collect the blackjack with the other cards?

Lastly, at the end of a round once all payoffs have been made, the dealer starts at 3rd base and then collects all the cards to first base and then collects his own cards last right?

Thanks for any clarification.

MJ