Your only limitation is pretty much your Data Transfer limits. Whether people download as Streaming (they hear while it is downloading) or whether they have to fully download it then listen to it, makes no difference. It all requires Data Transfer -- from the Server to their computer.
How big the files are.
How many people download the files.
How much Data Transfer you have.
These are the 3 main areas to be concerned with.
Helping people Create and Host their Web Site