Opera is a musical form, so you may want to use the Music Library, containing MSU Libraries' music collections, located on the 4th floor of the West Wing of the Main Library. It has its own web page, here. There is an “Ask the Librarian” link here, too, if you want help with music resources. Here are the major encyclopedia of music, a French opera encyclopedia, and two periodical indexes, to help you get started.
Dictionnaire de l'Opera de Paris sous l'Ancien Regime (1669-1791) Music Library ML 1727.8 .P2 D537 2019 t. 1-4
Covers the Paris Opera's repertoire, creators (compositeurs, dramaturges, maitres de ballet, costumiers, decorateurs et machinistes) and its artistic and administrative staff. For the first time, the entirety of opera productions are identified and their extensive staffing, with roles of performers. Many articles on concepts in this field.
For more music resources see the Music Best Bets page.