We are often asked about how many people you need to start knowledge management. Out of our experience we know, that our approach is interesting already for single persons and will be more and more attractive and effective as the user group grows.
So there is no minimum number of users.
Much more important are the interdependent tasks you want to solve in one solution. These tasks are often solved in locally optimized and independent solutions. Later on, the connection of these silos leads to insufficient and un satisfying solutions. No or small postive effect for the user is the result.
We have experience starting with single persons over groups and small companies up to organisations >1000 users.