From the jOpenRay point of view, there is no limits... but Windows XP Pro is supposed to be limited to 10 clients.
It's a good reason to choose linux as a server... or switch to Windows Server.
Wifi is fast enough for a single client.
About stability, from my personnal tests, the server will no crash if something wrong occurs,
but we have not enough feedbacks to say that the current version is production ready.
My advice is to talk to your Sun/Oracle representative to make them be aware that SRSS
is not fitting everyone needs and that jOpenRay needs their support (by providing protocol specification, expertise, ...)