Audio - import limitations

Start here for some details: http://docs.unity3d.com/Documentation/Components/class-AudioClip.html

I'm not aware of a filesize restriction. Number of channels I believe is limited to left and right (but I've never tried using files with a greater number than that).

So far I don't see any support for Loop Point meta date (common in .Wav files mainly).

So the work around is to trim audio to the exact loop point before importing.

This is fine and all but it could limit creativity in some ways which would force the audio to be trimmed before hand, and you may wish to experiment with loop on and loop off to get 2 different versions.

To trim audio before hand use a audio editor.