1: There is no blackout button. Make your own all ZERO value scene and name it BLACKOUT and assign it a button that you can hit quickly that you feel safe with. Put it at the beginning of your scenes so you can get it easy. In my case, I have "F" as my "Fade to blackout over 5 seconds" and my dash key as my immediate blackout. I don't want to use the space bar, it's too easy to hit. But, you make your own decision as to what key you want to use. As long as it makes sense to you, then that's all that matters.
2: Not really. It's best to do one set of fixtures and document. Then repeat with the others. Then make a new set of scenes/steps that consolidate those settings per step together. Use the FX Generator to help you make your effects, but pen and paper(or really good memory) to document the steps for replication. What I'd recommend is IF possible to match steps, say have one type of fixture doing a 6-step thing, and another fixture doing their stuff in 6 steps as well.
3: No. MyDMX does not support a music trigger or chase. You can, however, assign MIDI triggers to scenes and then trigger them via a sequencer. It's not a graceful solution because it requires a hardwired MIDI loop on a muti-port MIDI itnerface and properly setting up stuff in your MIDI sequencing software when done on one PC so as to avoid MIDI loops. Someone mentioned a software package that will emulate the MIDI interface. I haven't tested it. Then you can import MUSIC(say, you're using Sonar) and then input MIDI triggers when you want scenes to change/trigger.
If you really want to do this a lot(music syncing), I think CompuLive is the better package to go with. CompuLive supoprts MIDI bridging into the application which lets it work much better in this regards.
Or, you can assign your triggers to YOU pushing keys at certain times. Certainly the cheap way to go. Can't say it's the best, but certainly not the worst. Sometimes human intervention is the best way to go.