Steel Tracks instead of tires, Solar powered electric/ethanol hybrid engine, Mesh metal over windows. The car itself IS a weapon, so I wouldn't worry about supplementing that too much. Armor plating is a bit over the top, but truck-bed liner spray for all those squishy, goopy collisions during the 6 months it takes the dead to decay into uselessness wouldn't go amiss.
Flamethrower probably over-rated since Zombies are immune to pain, plus it's really, really impractical on a moving vehicle in any direction except backwards, which is probably the least important direction if you're in a car. Also fuel for Flamethrower could simply be used to drive car away from/over Zombies.
Collection of Personal Weapons for use when out of car would probably be better placed in passenger seat. Also seperate front and back seats with lexan like they do in Cabs in case you're feeling merciful enough to pick up some sidekicks who probably-are-but-might-not-be-infected and are really hot/funny.