Leds:
The 2n2222 will be more sound reactive, but not as bright without music.
General Led's:
Well, you're going to have to go with something small. Bulb LED's are pretty much not going to work, because they won't fit in the trigger.
Speaker:
That should be fine, only if you plan to remove the umd drive. 3/8 of an inch is pretty thick
Output's:
As many as your heart desires, within logical reason, though.