Importing your audio at runtime (meaning that the audio loads and you would or might use a preloader for the audio) will give you the great advantage of using audio of any length while on the timeline you are limited by Flash's memory. Research dynamic mp3 players online and you will come up with some topics. make sure to include searching for AS 3.0 in your query.
Yeah you REALLY don't want your audio files on the main timeline... load all the audio as external files using the sound class.
I'd also suggest you jump in and learn how to integrate xml into your Flash, so you can pull all the audio data from an xml playlist. That way, 3 songs or 30 songs.. it's still very simple to present a clear playlist choice to your viewers.
couple dozen or so songs... yet the audio player is only about 400kb! ... tiny!... that's because the songs are all external. Player is unique and customized for the client... all the controls you need.
And no... you don't need any type of a "preloader"... since the audio files bitrate are normally in the range of 160kbps - less than 300kbps bitrate. Of course this is assuming that you are using mp3 and not some monstrosity like a wave file... if you are.. convert it... right now! You DON'T what to be playing wave files as downloadable!
So if you choose a reasonable mp3 bitrate of 200kbps or so... almost all Internet connections nowdays are at least that fast and will download the audio file faster than it is being played.
Here is a very good source for mp3 player tutorial:
scroll down about 3/4 way and look for:
"Flash MP3 Player: Part 1"
should get you started.