To keep the rattling down, you will definatly need sound proofing or just some interior mat against the sheetmetal, make sure your lisece plate has some mat behind it too because they rattle like crazy.
You can put your head unit anywhere you want to. you can leave the stock one in the dash and just disconect it and put your new one in the glove compartment, its custom and its pretty safe. under the dash, n the center consol, on the ceiling, you name it.
As for crutchfeild don't buy anything from them they will overcharge you. Look around on the internet compare prices. I myself use Apex audio, they have good prices and a huge selection.