If your community grows too big, you might face a resource problem. You no longer have the staff to manage the community (or communities).
You have one of two options
1) Encourage the community to run and manage itself.
2) Get the resources to manage the community.
Option 1 is terrific when it works. You recruit and train volunteers to run their own community. There are some great self-governing, self-sustaining, communities.
However, it takes years for a community to reach this stage. Once reached, it is difficult to sustain and you sacrifice a significant opportunity to further develop the community.
Option 2 is better, but also difficult. Where do those resources come from? I suggest charging newcomers to join the community. Develop a revenue stream from the community that covers, or partially covers, the fee for a community manager.
If a community manager costs $50k per year, you only need 210 members paying $20 per month to cover that. This isn't an insurmountable challenge. Alternatively, develop products/services that the community is willing to spend $20 a month for.