— the most flexible option on the server side (although paid).
Users will be able to broadcast many ways. For example, trite, FMLE
However, about a "podcast" is not clear — you need a video blog like youtube, or live broadcasting, as own3d
? Although, in wowza you can "live" and "on demand" without problems.
In any case, the same server, you will not be enough. You need at least a couple of mega or a dozen so-so. And to fasten to them the scheme of balancing or configure the balancing in the most wowza.
Plus-authorised users — is generally a separate topic. Ready-made solutions that I know of. Still, projects such as youtube is not often that stamp, and the mass requirements in popular CMS for this case like has not yet appeared. But wowza quite possible to "make friends" with the authorization system of the site within a reasonable time, so I suggest you start to study it.