IDK if it's in any of the online repositories, but I use the menu class I wrote for Java, then ported to BGT. The filename is JMenu.bgt. It is, however, event-driven, rather than self-executing like dynamic_menu.
As for music, how cumbersome it'd be depends on what menu you're using, but mostly you would just say if (music.playing == false) playsong("menumus" + random (1, 5) + ".ogg");. Not exactly like that, unless you're using a sound called music and playing via a function called playsong, but that's the jist of the idea.
If you're using something like dynamic_menu, that blocks the script while it executes, you'd need to put that bit into a callback.

cant really help here. you can change the music every time the menu opens, but you can get an example of thaat in the cm source.
but since no one really uses cm source for anything, which would make it a clone! lets copy some wild blind tech code here
you need to put an int musictracks number which is the number of music tracks. you'll notice in your average menu.bgt, you'll have a void called setupmenu, in which there is a line, m.add_music("menumus.ogg");

we want to change this to:
m.add_music("menumus"+random(1,musictracks)+".ogg");
that's the basic idea
hope this helps!