A number of states HAD official religions when the Constitution was ratified, and the First Amendment was not understood do interfere with that. All such state religions had already fallen by the wayside prior to the passage of the Fourteenth Amendment, but their earlier existence is nonetheless worth noting.
Sorry, I missed answering your post in turn. -- See my comments on #9 about existing State sponsored religions being 'grandfathered in'.
Congress was specifically told to 'make no law' on that particular issue; -- which lead to the states rights crowd erroneously insisting that States did not have to honor the bill of rights.