In terms of when to buy and where, I can give you insight based on experience. I lived there from 2004 – 2006 and have a lot of friends there, all over the DC metro area.
My initial thoughts:
Keep yourself inside the beltway for resale value returns. Outside of the beltway has taken a major hit and will continue. We lived in alexandria, bought in Northern PW county in 04, sold in 06 at the height and now the homes is 100K less than we bouught for in 04.
I know some solid parts of arlington that are single family areas so let me know if interested. Alexandria is nice but overblown in my opinion. I liked fairfax/ fairfax station but that may be too far out. You could probably get away with just over the bridge into maryland too. Vienna is nice but not sure what your budget is.
