Thanks a bunch, TheMathProf.
Maybe Moneylender to trash Copper helps, but, but then again, he wants those Coppers for his Stables. I figure that with enough Stables and Counting Houses, maybe, just maybe, he can make a living on ditching Coppers to the Stables only to pick them up with Counting House. That does seem farfetched, though. Stables also should help cycle his deck to find the Sea Hag more, in theory. In practice, probably it doesn't have much of an effect. Moneylender adds no more money than Silver, so I also think that would have been very unlikely to win, especially with Colonies in play. Counting House makes purchasing Colonies possible, I guess?
Still, I doubt I managed this well. I am still confused, hours after the game has ended.