Reading between the lines
This is a bit speculative, but I think Saul changed his name to Paul at this point, not when he was converted on the Damascus road. Verse 9 isn't an out of place "oh, yeah," on Luke's part harking back to his conversion. He changes it to mark the Roman governor who believed at their first stop, and took a deliberate strategy of going to the Gentiles (though to the Jew first). This explains the name change being mentioned here, and John Mark's departure.
- When the Spirit leads, it isn't always some extraordinary and unexpected thing. Barnabas went HOME for their first missionary stop.
- The apostolic witness to Jesus' resurrection remains central, though Paul didn't see it. He points to their witness.