Q: Is there a minimum number of worshipers required before adoration can proceed?
A: It can be as few as one or two. See Holy Communion and Worship of the Eucharist Outside Mass 90. But a priest is not supposed to expose the Blessed Sacrament for his own private prayer. Any exposition should take place according to the ritual – proper vestments and incense, for example. The idea is to keep the solemnity of the experience even when only one or two people are there.