1. I think it depends on which uPnP Server Software you are about to run.
On my 500gx runs a Twonky Vision uPnP Server.
Go to the Twonky Vision Site an have a look on the supported Players.
I think every Streaming Client should work (noxxon or whatever)
I can handle the Stream with Nero Showtime.
It´s the only Player i know so far which supports uPnP.
2. dunno
3.dunno. try