> How much of this could be automated for LaTeX?

All of it, probably? It depends a bit where you want the automation to
start. You describe three `paragraph styles' called `b' `c' `d'
(perhaps there is a fourth, `a' ? Hart's is in the library across the
road:-) Probably each of these could be set in TeX.

It becomes hard if you need to make the choice of which paragraph
shape to use automatically, ie do you know that for a given class of
documents you can set all footnotes run on in style `d', or do you
need, on each page, to inspect the texts gathered and decide a
`suitable' paragraph style for setting those texts?