I think there was already a thread where the default size for mobile devices were displayed, I don't remember where it was though, guess you'll have to search the forum to find it back.
About sound, well. Sound support in HTML5 is pretty bad in desktop and even worse on mobile, so it is likely you did nothing wrong and it's just the iPod device that can't handle it.
From what I've read so far about mobile, it appears that iOS5/iPad2 is the best device, and performances there are pretty bad.
Also I guess you could have a look at the tutorials about mobile devices (such as this one
, this one too
and this one
about screen sizes).