Apple claim QTSS on a G4 can handle 2000 simultaneous streams, and while I believe this to be grossly optimistic, any G4 server will have sufficient horsepower to run a reasonable number of QuickTime streams and should be a good choice based on your description.
The 10-client version is all you need - the client license only relates to AppleTalk-based clients, not web-based ones, so you can still serve more than 10 users via http or qtss, even with a 10-client license.