Not sure about your idea #1, but 2 and 3 could be fun.
I'll also resuggest my idea:
Since the Zombie Apocolpyse is all about hordes of undead shambling relentlessly after you, and your own dead rising against you...
The Zombie AI doesn't launch waves, instead it continuously streams zombie ships from the AI homeworld straight to the human homeworld. The never stop, never hesitate, just keep coming... AIP would determine spawn Mk and rate/clump size. For added fun, make all ships spawned this way also become zombie reclaimers.
You'd need to have serious defenses if you let the AIP rise, because you'd NEVER catch a break, no time to refleet, send your defenders off on offense, etc.
You could probably implement this using mostly existing game mechanics if you treated the Zombie AI as spawning a small Zombie exowave every 30 seconds, minute, whatever. Start with each ZExo being a dozen Mk I ships. By AIP 1000, you could have Zombie reclaiming H/Ks leading their Zombie reclaiming Golem brethren to eat your face.
Another idea - Have a in-system AI only structure that causes all non-zombie ships that die in that system to respawn as Zombies for the AI? A Core Undead Guardpost? The icon could look like a tombstone.