See Shulchan Aruch Even HaEzer Siman 1…discusses multiple wives at length. the S.A. recommends not more than 4. Grandchildren from Baba Sali’s 3rd wife live in Lakewood. There are those who have multiple wives today. The known ones have a “legal” wife. and the others are friendly to the first and live together usually with {private) Chupah and Kidushin..ie… not registered with the government…so she appears as a “live in”. Others have a “wife” in other countries whom they visit for extended periods. The Vilna Gaon is noted as saying that there are 2 things that are “meakeiv haGeula” stop the redemption of the Jews… 1. that Ashkenazim stopped Birchas Cohanim, which he and his talmidim tried to re-start, and were successful in Eretz Yisroel… and 2. the Cherem of Rabbeinu Gershon forbidding multiple marriages, which he explained was only accepted because of the goyim, and was not a Jewish concept. See the Cherem which says so specifically