It's a standard single DIN size which is probably the most common. There are a lot of double DIN sizes out there now too. On first glace it looks like yours might be a 1.5 or something. I would go to Crutchfield.com or call them to get a kit for this unit and you car. You'll probably get a little storage shelf underneath the radio.
It will fit if you modify your vehicle, which you probably don't want to do. Here, go to Crutchfield and they will tell you what will fit your car. Then come back to Amazon to buy it and get a better price for it. http://www.crutchfield.com/p_1303400UB/Pioneer-DEH-3400UB.html?search=Pioneer_DEH3400UB&skipvs=T
Yes. You will need an installation kit and harness. The kit has a junk tray that mounts to the bottom and fills the double din space the stock stereo occupies. I also recommend a installtion harness as well. Saves a lot of testing and messy wiring. You shouldn't have to use an antenna adapter. It should be standard motorola, not the mini chevy used in the 90's.