Indeed, this is the direction I'm heading. However, I'm doing it by
hand first so I can refine my methods to a point I'm satisfied with,
and then build the automation afterwards, hopefully doing it right the
first time. [...]
IMHO this is exactly the wrong way round: Pick one of the existing formatters (hindent, brittany, ormolu, ...) and stick with it for a while. If you don't like what you see, you can try another one. But the main point is: These formatters embody good practice learned the hard way from lots of other people, and using them will make your code more readable not only by you, but by others, too. The "not invented here" syndrome is seldom a good idea, and consistency is far more important than small details you might not like.
Cheers,
S.