As for unillustrated paper book, 18 cm x 25 cm, 464 pages, 29 fascicules x 16 octavo sheets = 464 pages
The best options to get a PDF file of high quality and small size (light weight):
Black & White
Brightness 195 (or) 200 of 255, and not (128) at all
Brightness degree likes the eye concealer, whenever it became high, whenever it covered the brown & yellow spots & shadows in the old paper.
So, increasing brightness of (white) background, and therefore decreasing boldness of (black) letters & words, give a pure page, also a lesser size of scanned paper.
The only problem in the (High) brightness is with the letters which are not full (enough & well) of black ink (the wiped old words). Increasing brightness (degree) effaces them.
As for contrast between black & white, it is adjusted automatic.