The visual dictionary puts the Sith Eternal Fleet in the “hundreds.”
I am hoping the novelization will mention of the Fleet compositions further. And if Sith Fleet were under crewed.
As it stands, with the exception of their Flagship, the First Order’s Fleet assets were spread around the Galaxy during the battle.
**The assumption here is a high percentage of those vessels were non capital class ships.
(257 ship model renders were used, including the Fireball, Jarek Yeager’s racer, and Torra Doza’s ship, and mining guild freighters from Star Wars Resistance, as well as ship renders from The Clone Wars and Star Wars Rebels.)