[Disclaimer: I'm not a lawyer nor passed thru the same process, so please don't take the next words as the Absolute Truth]

About the nationality issue. I have heard in other forums many times that renouncing to your US citizenship is just a formality and that this declaration you sign is never sent to any US office, so the US Government don't know you've done that and, thus, you can keep your US passport forever. A friend of mine gone into the process of getting the Spanish nationality via 10-years-of-legal-residence and I know for sure that he keeps his US passport, too.

See these two Webpages (one from the US Govt.):
http://travel.state.gov/loss.html
http://www.richw.org/dualcit/law.html