Ark community servers are multiplayer servers that are hosted and maintained by the community. This allows for a more customisable experience while playing including modified server settings, better support and even new features.
Ark servers have no maximum amount of players for dedicated servers, you are only limited by your servers hardware.
The minimum requirements to host an Ark server are 8GB ram and 20GB disk space, but you will want to exceed these requirements for a better experience and to give the server room to grow.