Regardless of the team size, I say simplify as much as you can so you can dedicate your resources customizing what makes their business special. You mentioned a PBX system and no infrastructure, this makes me think you talking about Customer Management. It sounds like you’re documenting as you go, fantastic. Maybe loop in a noob time to time to review the documentation or have a Q&A that reifies the docs. Best of luck!
Communists are just as selfish as anyone else. Their point is that if we want a better life we need to move beyond capitalism, communism is an appeal to our selfish nature as much as it is a call for cooperation.