You are supposed to get less interferance from the engine if you run the wires to the battery as opposed to using the 12v power source. I don't really know what the difference is, I have it from the power source in my F-150 and you can get a little static with the engine on that goes away when the engine is off, it one of the things that is on my not so pressing to do list...
My dad had a cb mount that sits on the tranny hump, it has a speaker mounted in it and angles the cb up. It was sitting the garage so I nabbed it and it looks really good, with the 12v power source I can rip the whole thing out quickly if I need legroom for the middle seat. Most newer vehicles are not very friendly to mount a CB in unless you luck out and it will fit in the ash tray (mine is also my cupholder so that wasn't even an option)
Truckstops are a good place to get CB stuff, I got my cable, antenea mount and antenea at one. I have a 3' tunable tip Firestick, I would like to get another for more range, I think I go about 4-5 miles the way it is now.