Well, it took a while, and a lot of testing, but I now have all the pieces in place. Postfix, MySQL, Courier IMAP, Postfix Admin, and virtual domains, all working together. See my prior posting for links to the various packages and more tips.
The last hurdle I took care of last night, eliminating the old mailbox format accounts on my server, and instead going with maildir format accounts that would work properly with all the above software. For anyone setting up a new server, save yourself some trouble and use the maildir format from the beginning.