I don't think you can do all your shopping online. go to some stores that can not only sell you the equipment but can do the installation and get recommendations and prices. then you can go online and research the quality of what they are suggesting.

speakers come in fairly standard sizes so you ought to be able to figure out the sizes with a tape measure. get a rough measurement and then compare them to what you are seeing for sale.

sounds like you want to buy a radio that will fit your dash and has an I-pod connection. sites like crutchfield will let you end your car model and then show you radios that will fit.