Much as institutional church leaders may hold
strong dogmatic viewpoints as to what constitutes a legitimate
"church", the Bible really doesn't have much to say on this
question other than what the word "church" means in the original
Greek. Namely a "church" as simply an assembly of believers.
Other than Matthew 18:20, the Bible doesn't give any indication as to how many believers have to be assembled for the group to be considered a "church". But if we take Mt 18:20 as the standard, Jesus says, "where two or three come together in my name, there am I with them." Well, there you go.
There is the implication that the assembly be a
regular meeting. Doesn't say how often the meeting must take
place for the assembly to be considered "a church". Though it
does say, "encourage one another daily,
as long as it is called Today:" Heb 3:13 "And let us consider how we may spur one
another on toward love and good deeds. Let us not give up
meeting together, as some are in the habit of doing, but
let us encourage one another— and all the more as you see the
Day approaching." Heb 10:24,25