You only can't import audio files like mp3 or wav @Disco, but that makes more sense that you do this elsewhere also.
try to edit the instruments too
of course you can use MIDI with a free account xD
pretty sure you can make a midi and post it but I'm not sure about downloading a midi, other than importing it.
All Original, I don't think you can do MIDI with the free account, but I do sound design other places as well; so this isn't really my first time.
Is this an imported MIDI or did you make this yourself? Either way, good first track :D