The battery he is talking about is the Receiver battery. It's a battery pack instead of having to replace the AA's in the truck. Your hobby shop will have them in stock, ask them about the receiver pack.
Get the 5308 version of the revo. It's got a few upgrades on it from the factory (17mm wheel hexes, Single Steering Servo, 150cc fuel tank, good air filter, etc.)
Yes, clean your air filter element after your break in, and after every hour. You only have to clean and oil the outer element every hour, and you can do the main filter every 3 or so, depending on where you drive.
I would get about 5 extra glow plugs, and maybe a spur gear or two. I bash mine pretty heavy, and I haven't broken anything yet.
I would go ahead and get a Glow ignitor too. The EZ Start system heats the plug, but the blue wire is easily damaged, so I would go ahead and get that.
I would invest in a decent set of tools, a 4 way glow plug wrench, and a nice set of hex drivers at minimum.