Take a lok at this

You need to have the stock binary /sbin/init file replaced by a script
so that you can add the command(s) to run visualizations prior to
starting the player. You may want to look at the VolAdjust/Picker
package, which among other nice things give you a sh-script to replace
the binary /sbin/init. Good instructions too!

I don't think there's a VolAdj package for the 1.03beta series, but
I'm sure there will be once it's out of beta.

As to boot up sounds, I don't know anything specific, and don't know
if an ordinary mp3 player compiled for arm would work. Maybe the
SID player
could be pressed to service if you can make the sound you
want in that format.

/Michael