Armies of Middle Earth during WotR

[Tuor in Gondolin]

An interesting topic which needs more time for research and consideration.
I think some estimates may be low. For example, I'd view Dain's 500 at
the Battle of Five Armies as a rapid relief force, not a reflection on the
total he could amass (somewhat analagous to Theoden's not having
time to gather Rohan's full strength).

Have you consulted Karen Fonstad's The Atlas Of Middle-Earth ?
She has some interesting detailed breakdowns of forces (particularly
good guys, at the Hornburg and the Pelennor Fields).

Btw, I've been reading The Siege of Vienna , by John Stoye. Do
you think the 1683 siege and relief was an influence on Tolkien, there
is an interesting paarallel in both the siege and the relief, including
the gates to Vienna being virtually battered in.