1. that is a matter of opinion.. my atom setup got outgrown within a year of building it(granted, i also run audio processing)..
for 'most' setups, a atom-based netbook should be fine...
2. the most common option seems to be hardwired cig-lighter adapters off ebay..
3. the faq's:http://www.mp3car.com/vbulletin/advfaq.php
otherwise, search around for other netbook installs-- i know i have seen a couple..