Ignore M3U files altogether. They are not music, but are just text describing
where the real MP3 file is located.

Uploads of any music file will take a long time on dialup because it is so slow.
There's nothing you can do to speed it up, so you might as well start the
upload at bedtime and let the computer disconnect itself when done.

You could shrink the music files a bit more but the sound can suffer a serious
loss in quality and the process can be a bit confusing. Pkay around with it,
learn how it works and see if you can get a good sound.