Can I add my own songs? What kinds of sound files can ChurchBells use?

You can provide your own music.  Please make sure your sound file names are not long file names, and no spaces.
Don't worry; you'll get a chance to describe the tunes better.  Your tunes should be in WAV, MP3 or MP2 format.
If you use another format (like OGG) you need to make sure Winamp can play it, and create an M3U file for it.  Then
ChurchBells will play the M3U file by passing it to winamp at the right time.  Winamp is not needed for WAV files.