On the other hand, there is a risk with building too small and too soon. It can actually inhibit the ultimate growth of the congregation.
Usual practice (and I've been through this twice) is to build a "worship space" that can be turned into a parish hall.
Both my former ECUSA parish and my Catholic parish did this. I've watched it happen over a period of about 45 years, because I went to the elementary school attached to our former ECUSA parish, and I grew up literally two blocks away from our Catholic parish.
The ECUSA parish started with one of those buildings with the exposed L-shaped structural steel beams (cheap). With moveable dividers, it became classrooms for the school on weekdays. It eventually became the parish hall, then the auditorium for the school. The Catholic parish started with a hilarious low, round concrete building (locally known as "The Great Pumpkin") that eventually became the gym. The second building started out as the sanctuary, then became (and still is) the parish hall. The current chapel was added as one wing to that building, then another wing was added as Sunday School rooms. The new sanctuary was constructed at the other end of a covered walkway from that building -- it's a "real" traditional brick church in the H.H. Richardson style.
Except for the "Great Pumpkin", which was wrecked out to construct the traditional Oxford-University-style buildings for the new prep school attached to the parish, all the buildings survive and are functional today.
Our current parish is at 1600 households, which exceeds the growth estimate made back in 1988.