Further follow-up, for those of you following my search for my wife's ancestors...
Peter Post, who sent me the note regarding the Beachwood Cemetery as well as information about Elder James' daughter Mary Post, sent me further information which strongly suggests that Alexander Flandreau, born 1820, is the son of Elder James Flandreau.I have modified the database accordingly, as well as adding Alexander's brother Irving as a son of Elder James.(I've been wondering whether the Irvings and Ervins and Irwins are variations on the same people.Hopefully I'll know more after a trip to New Rochelle in the coming months.)
I also made a trip to the local Family History Center and picked up a few new names I hadn't caught before.They're in the database as well.
No new obvious leads on some of the larger Flandreau mysteries -- the mid-eighteenth century, the ancestry of David Flandreau of New York City, and that sort of thing.But I'll keep looking.