Not all singers or instrumentalists need to be soloists. They just need to be good enough. You need some soloists who are not prima donas, who are team players. They will carry the team and set the standards of excellence and mentor other musicians on the team. Quality depends in part upon the team you build, the community that is happening.
Relationships are very important.
Also, addressing spiritual growth is important. It doesn't have to happen formally, but portions of every practice should include relationship building and faith formation. That's pretty tough with artists, but VERY important. When someone is off pitch, they need to be told it. When someone misses the riff, or is playing off rhythm, they need to know it.