[App_rpt-users] Hub vs Node?

What if anything are the specific differences between a single node (tied to simplex, repeater, Pi box and headset...) that can presumably only accept one in-bound call/connect, and a hub, to which many can connect and bridge through/over? Given a certain amount of specialization or purpose/interest-built hubs I am interested in having a purpose-built hub for a few systems and users not exclusive but so as not to impose on others' hubs and traffic. What does it take to do this?