Staying with my 2007 Ford Taurus

I was seriously hoping to buy a new car in the next year, but the economy is not cooperating. I think I have 5 more good years with my Taurus, but I would like to spend some time to make riding in it more enjoyable. I have found answers to a lot of my questions on this forum simply by searching - thanks for letting so many smart people join up! My question now is about speaker placement. My T comes with speakers in the front door and speakers in the rear deck. I have been in upscale cars (BMW, Lexus, etc) that also put speakers in the front dash, in the rear doors, on the ceiling (usually small box enclosures). I think have room for speakers in my rear doors. I think there is also room in my dash to mount speakers as they are mounted in the rear deck. I am going to pull my dash apart in a week or two to replace my radiator core. I listen to a huge variety of genres - good bass is essential - maybe a subwoofer? I am not that familiar with the mechanics of sound, but I know good sound when I hear it. As I disassembly my car, piece by piece, my plan is to add sound deadening paint - maybe also some insulation as well. I am even going to replace the carpeting in the vehicle. I have also seen small speakers - maybe 2"? mounted in a small enclosure on the panel that holds the side mirrors.

I would appreciate any suggestions you have to help me develop the speakers in my sound system of my T. I will probably at a later date go with a double din stereo - I think that will support a backup camera as well - but I want to focus on the placement of the speakers now because I will be taking many parts of the car apart to add the sound deadening, replace carpet, etc.