Are there any commentaries regarding the first disciples of Christ already being disciples of John?

In studying through the gospels chronologically, I realized that at least two of the apostles, Andrew and most likely John, were already close disciples of John the Baptist before they met Christ. Andrew went to get his brother Peter, which implies he wasn't far away. It occurred to me that, at least for the inner core, these first disciples of Jesus did not start following Him out of a vacuum. They were spiritual men and were most probably seeking for the Messiah, as directed by John. It seems worthy of note. I could not find any biblical commentary on this , to get more information. For example, where was John baptizing? These were working men; yet they were hanging around John, away from home. Bathabera is traditionally considered to be near the north end of the Dead Sea and east of Jerusalem, and about 70 miles from Gallilee. This makes sense considering John the Baptist preached in the wilderness, and Christ was immediately led out there after His baptism. I would like to know, besides if there is any commentary on the first disciples before they met Christ, what is considered a reliable current source for ancient geography. Thank you.