The search feature on this forum will turn up a lot of results that should help answer your questions.
A lot of people upgrade the sound system, however subwoofer locations tend to vary because it is depends on how much space you are willing to give up. Normally under or or behind the passenger seat, in the passenger footwell, or above the engine. The CD tray can be replaced with another shelf, or a custom gauge install. Which ever option you choose, you will have to custom paint to match. It looks like a previous owner had the dash painted guards red, it could also be a factory option.
