Not sure if I like anyone in your FA pool. You might want to see who is in need of a catcher in your league and see what pitching they have. You might be able to trade Varitek + either Buherle or Garcia for a higher rated pitcher.
If you are looking for Jose Reyes, then I would package Buehrle and a bat (most likely Renteria) to try and get him, but I think you are going to have a hard time getting Reyes, whose value is VERY high right now. I agree that you should be looking to upgrade at SS, but I'm not sure you need to shoot as high as Reyes. Guys like OCab or Furcal could be better options that would require you to give up less.