I set up a similar system in a current project and it works pretty good so far. There are 10 songs in the game; upon import, I renamed them to "1" through "10". The game starts and I call 'Play str(round(random(1,10)))...' and add a condition 'On music ended...' (or whatever tag you give the music) and the action 'Play...' with the same settings that started it off.
I used a Function in this case; at the start of the layout, the music function is called to play the first random song; when a song ends, the Function is called to start a new random song.
If you want to stop songs from repeating, add a variable that records the name of the last song played and compare it before starting a new song.