In addition to being an apocalypse and a prophecy, Revelation is also a circular letter, sent to seven churches in particular. John does not exactly say that he has been exiled to the island of Patmos, just about forty miles into the Aegean Sea from Turkey, but that is the tradition and it is a reasonable inference.  The Romans sometimes used exile as a form of punishment, and we know of other places where they used islands exactly for this purpose.
John has a revelation from Jesus on a Sunday, the Lord's Day. We have every reason to believe that the earliest Christians celebrated the resurrection of Jesus on Sunday. In addition, Jewish believers would likely have also worshiped on the Jewish Sabbath, from sundown on Friday to sundown on Saturday. Then on Sunday morning, before dawn, they would worship, also coming together to eat at some point during the week. 
While it has become common for Christians to consider Sunday the Christian equivalent of the Jewish Sabbath, there is no evidence in the New Testament that the earliest Christians thought of the Lord's Day in this way. In fact Paul himself tells Gentile Christians that they should not be troubled about whether or not they keep the Jewish Sabbath (e.g., Rom. 14:5; Col. 2:16). Christian Jews might not work on Saturday, but we have no evidence that there was any such prohibition on Sunday for either Jewish or Gentile believers.
John has a vision of the risen Jesus on Patmos. Since the Book of Revelation is imitating the form of a Jewish apocalypse in some respects, some of the features of John's vision may not be meant to be taken literally. For example, it may be that the letters that John writes to the churches are not exact dictations from Jesus but are actually more like the way the other parts of the New Testament were inspired, where the personalities and thought categories of the authors were involved. There is room for both views to be held by individuals who believe Revelation is inspired and inerrant. The issue is only about what was originally intended.
The seven churches were all in western Asia Minor, the western part of modern day Turkey. Although John specifically addressed these churches, no doubt it was understood that the entire region would read the book. John goes from one church to the next in what was somewhat of a circle, starting with Ephesus and moving north to Smyrna (modern Izmir), then Pergamum in the north, then going inland and down to Thyatira, Sardis, Philadelphia, and finally Laodicea.
In the past, some have taken these churches as an allegory for various periods in church history (a historist interpretation). In this interpretation, Ephesus represents the church of John’s day and the church of Laodicea represents the current of our current day. Then the various churches in between are made to fit various periods of church history from then till now.
On the one hand, this is a very suspicious interpretation. After all, these were real churches, and there is nothing in the text of Revelation that suggests anything like this sort of meaning. Indeed, Revelation much more gives us the impression that its events are in the near future (e.g., 1:1). In fact, no one would have thought of this interpretation until about now in history. No one in the year 1000 would have thought, “I wonder if we’re in Sardis yet”…
 Revelation 1:9 says he is on the island "for the word of God" and the "testimony of Jesus," as well as that he is a companion in suffering to the churches to which he writes. See ***
 For gathering before dawn, see Pliny the Younger, Epistulae 10.96. 1 Corinthians 11 and Jude 12 suggest a common meal was customary.