What is the "128 font limit" in classic Mac OS?
As per http://www.wikiwand.com/en/Fonts_on_Macintosh, System versions 7 to 9 supported a maximum of 128 font suitcases and each suitcase could store multiple fonts.

However, according to http://laegernelipkesgade.dk/Fonts/kptype/Kontrapunkt%20Typefaces/README.txt
Macintosh System 9.x allows you to open 512 suitcases at once. Macintosh System 8.x and earlier only allow you to open 128 font suitcases at one time. If you exceed these limits, not all the fonts you install will work.

If you search for "128" you should find the above statements.