StarCraft 2 - "Trapped in Hell" custom map - tips?

[mikeymikec]

It's a 6v4 CPU multiplayer map that I've been playing for a while now, and while I've 'won' the map a few times (mostly because of the efforts of better players), I don't have any particularly sound strategies myself yet. Any tips?

One thing I haven't figured out yet is how to make Nova do rapid fire.