I've had lots of questions recently and no time to really get answers and post them up here.  If I haven't answered you question it's because I don't know the answer and haven't had enough time to get to the bottom of it yet.

First of all I had a couple of questions on MSAS which I don't know that much about.

Can I tell which tuner is being used when a recording takes place using MSAS? No, you can not.  What you can do, which may or may not help is use OnTVRecordStateChange from a background add-in which will give you a GUID and you could track which was in use - this won't help if a tuner is being used for live TV though.  Here's a code snippet on how to use OnTVRecordStateChange:

void IAddInEntryPoint.Launch(AddInHost host)
{

host.Television.OnTVRecordStateChange += new Microsoft.MediaCenter.AddIn.TVRecordStateChangeDelegate(TvRecordStateChangedHandler);

...

}

public void TvRecordStateChangedHandler(object obj, Microsoft.MediaCenter.AddIn.TVRecordStateChangeArgs TVArgs) {

if (TVArgs.Started)
mcHost.HostControl.Dialog("Recording started on tuner " + TVArgs.Tuner, "TV Recording",1,10,false);
else if (TVArgs.Stopped)
mcHost.HostControl.Dialog("Recording stopped on tuner " + TVArgs.Tuner, "TV Recording",1,10,false);

}

Can I use remote desktop to connect to a Media Center PC? Yes.  You can even use Media Center, but it won't play video over a RDP connection

Can I use animated backgrounds in an HTML page? Not really a media center question, but I don't see why not, use an animated gif.

Could I create an add-in that played a selection of WAV files with a gap between them? Yes, using Playmedia and Playrate you could contstruct an addin to do this - waiting until the playrate was stopped, then wating however long you want before playing the next file.  You could also use More With This  to make this work with any folder of audio files.

Can I use ASP.NET for development?  Yes.  You can use any web technology that outputs HTML.

Can I use WinForms for development?  Yes, but if you're running as a .exe you won't have access to Media Center APIs.  If you're running as a .NET applet in a webpage you'll have access to the Media Center APIs from the HTML page and will have to communicate between the page and the .NET applet to use the Media Center APIs - non-trivial to do, but not hard.