The 2008 Sora line has been revamped as is now a 9 speed setup, so the upgrades shouldn't be too difficult now.

http://cycle.shimano-eu.com/publish/..._groupset.html

Consider the type of rides you expect to be doing and the timeline. Going used will get you a better bike for the price, but it's not a good time right now. I've been looking for a 48cm WSD bike for a friend of mine for a month and haven't seen anything locally. Even the craiglist link has a post about wanting a 48cm bike.

If you're doing mostly flat rides, the weight of the bike won't be much of a concern.

Just my .02. Good luck on the search!