Okay, so they put out a silly sourcebook. That invalidates the whole line?
Honestly. AFMBE is the
best rules system for zombie gaming I've ever seen. And the wrestling stuff is in a supplement you don't have to buy!

Plus, the new edition of the core rulebook has a conversion appendix for d20.
For pure d20,
Blood & Brains is a good book. Has a few silly things, is very strongly inspired by
Evil Dead /
Army of Darkness, but has a number of very fun rules and ideas in it. It's also very cheap.
Haven't checked out
Year of the Zombie yet, though I plan to.
3)As for modules: I'm only aware of a few, mostly for fantasy gaming. Check out the Wizards' website for free adventures, I know there are a few zombie/undead focused ones.
Pick up the old Ravenloft adventure for D&D 2e,
Night of the Walking Dead. Classic.
4) Mass combat rules are very uncessary. You generally only need rules for you PCs, and however many zombies they're dealing with at the time. Massive combat is generally best left to GM fiat: "As you look out the window, you see a platoon of Army personnel firing frantically at the oncoming horde. Body parts are flying everywhere, but the zombies are relentless..."
5) The Zombie Survival Guide is a great non-RPG resource for the subject. It's written tongue-in-cheek, but it actually makes some good points and has tons of ideas for your campaign.
The NCRPC site & free PDF are both great ideas as well.