I prefer to inlet the barrel separate from the breech plug. Once I have the barrel inlet, I then seat the breech end of the barrel to the stock. Once I have a good fit between the end of the barrel and stock I install the breech plug and inlet it. I like the idea of having the barrel seated prior to inletting the flared plug, less chance of unsightly gaps in the tang. Of course, I am deliberative and prefer doing one thing at a time. I inlet my locks one piece at a time as well.
I am sure the majority of the answers to follow will lean towards inletting the barrel and tang as a unit and the lock as one piece to save time. Everyone wants to say they are like Mark Silver since he came out with his DVE on traditional gunstocking. As for me, no one ever questions how long I took you to do something when the results are stellar.
David