1. Yes. The HU should split up a simple stereo into whatever it can output.
2. Measure your dash to find out.
3. Cheap does not equate to good. Ebay = cheap. mp3car store = good.
4. See #2.
5. Search the forums for ideas.
6. Search the forums.
Someone needs to take a stroll through the FAQs: http://www.mp3car.com/vbulletin/advfaq.php