On Rosh Chodesh and chol hamoed, four men are called to the Torah – no more and no fewer – and a haftarah from the Prophets is not read. The first one called recites the bracha before reading the Torah and the last one recites the bracha after the reading. The general rule is that if a day has a musaf service and is not yom tov, four men are called. Five are called on yom tov, six on Yom Kippur and seven on Shabbos; these numbers may not be decreased but they may be increased and a haftarah from the Prophets is read. The first one called recites the bracha before reading the Torah and the last one called recites the bracha after the reading.
If there is no minyan, they do not go back and repeat the Shema when one is formed, nor do they repeat Shemoneh Esrei, duchen, read from the Torah, read a haftarah from the Prophets, perform the stations at a funeral, recite the blessing and consolation for mourners, recite sheva brachos for newlyweds, or bentch using God’s Name in the zimmun. When redeeming consecrated land, we require a minyan of nine Israelites and one kohein; the same is true when assessing the valuation of a person.