When you run HDF on a single machine it is a single JVM process. That instance has three internal repositories (content, flow file, and provenance) which are what can be controlled in the configuration as to how much of the repositories is retained on disk. For high performance it is best to have each of the repositories using a separate disk.
One instance can have many logical flows which can be optionally grouped inside processors groups. There can be many disconnected logical flows with in one instance. There are discussions for future capabilities where logical flows could be restricted to only certain groups of users.
The default for memory requirements for NiFi out-of-the-box are 512MB, so at the moment that would probably be the starting point for an edge node.