We never grow up do we

I currently run a 400+ bhp evo 9 but im getting itchy feet.
Im seriousley looking at buying a 2006-2007 RS4 Avant
What i hope to get from you guys is the below please.
(1) What to look out for when buying.
(2) What does the car come with standard and what are all the optional extras.
(3) What should i expect to pay in this current climate.
Thank you
Richard.