Does it matter who “officiates” the baptism? Does it have to be a pastor?

Of course, the answer depends on which view of baptism you hold. Believers baptism is more an act of devotion on the part of the individual, so it can be done in a wide variety of settings. Covenantal baptism marks someone’s entry into the covenant people of God which gets its visual expression in the Church. For this reason, a formal representative of the church ought to be involved in the baptism, providing adequate explanation of the sacrament so everyone present grows in their understanding. In our denomination, Elders (who are both “lay” and “clergy”) are viewed as the appropriate representatives of the Covenant community.