To get a 10x smash chain you need to hit as many individual items as possible when you first go into the center of the intersection. A good technique is to hit consecutive lampposts until you reach the chain.
It may seem as though the Fighting Back and Hat Trick achievements should unlock at the same time. However, Autolog Recommendations and Autolog Challenges are different. For the Fighting Back achievement you need to respond to a 'Beat You' notification and subsequently beat your friends score.