It is generally a good problem to get too big. In other words, if there are a lot of people in the house church, it is usually a good problem. However, that is not a good enough reason to multiply. There must be mature enough people (biblically qualified elders) to begin a new house church. If there are qualified leaders to be sent to start a new house church, we praise God for multiplying his kingdom.
Sometimes, a house church will get filled with people who just enjoy being around each other but are not growing spiritually. This is a problem! If a house church is neglecting to make disciples who reproduce, this should not be replicated. It either needs to begin making disciples who make disciples or close its doors. Jesus also sent people away who were interested in being with him but who did not want to commit to his teaching. (See John 6)
How does a house church train up new leaders?
Through discipleship, every church member is being encouraged to grow in their walk with Christ constantly. There are some who will aspire to become an elder. Elders are encouraged to meet monthly, while including those who want to become an elder. Through deeper accountability, elders will ask questions of each other, pray with one another, and share the teaching time during worship gatherings.
Would the house church ever have the goal to meet in a large building?
The goal of the house church is to multiply reproducible house churches. The goal is not to get bigger meetings or buildings. We think biblically and practically the best way to grow God's kingdom is through reproducible house churches.