I did this while working on an OSS project. I used slack starting with just 3 people including myself. It eventually reached 4k members. At that scale it's no l

I did this while working on an OSS project. I used slack starting with just 3 people including myself. It eventually reached 4k members. At that scale it's no longer community but instead a support channel. Keeping groups small or interconnected is really important. Each person joining really needs to be an invite from someone else already in the group. Community also implies each member adds value. Again if you use invites it's reputation based. If any random person can join that's a dilutive effect. Long term if a community stays small or private it maintains what it always had but people might outgrow it or it may no longer serve the same purpose. If you want to grow and evolve then there really needs to be some shared values, goals, beliefs that continue to be the core pillars of why the community exists and what new members look to when they arrive.