The current world deadlift record is over 500 kg [1]. However, for mere mortals, guidelines recommend not lifting more than 25 kg unaided. If you want to lift more, it would be wise to get a friend or colleague to help, or to use tools, or to apply powered machines.

Similarly, in exceptional circumstances, a person can retain something like up to 150 relationships unaided [2]. In practice in day-to-day where people are members of multiple organizations and social circles, don't expect someone to maintain anywhere near that amount of relationships within your community. If you want them to interact with more people, they will need help of friends, organization, tools, and/or powered communications equipment.

If you allow a community to grow unchecked, unmanaged, unplanned; then yes, your community will likely collapse under its own weight.

However, with a good study of modern equipment and organization methods, and a lot of work and dedication it is possible to grow a community to almost any arbitrary size. But if you grow a community, you need to add more organisation and mechanisms to keep it working; as a result the nature of the community will almost inevitably change to some degree. Keeping a community quite as fresh and wonderful as when it started is most definitely an art form that -to my knowledge- no one has quite yet mastered.

[1] https://en.wikipedia.org/wiki/Deadlift#World_Records

[2] https://en.wikipedia.org/wiki/Dunbar%27s_number