You should play Trails from Zero and Trails to Azure. You played CS4, so you'll know what's happened since, but it's basically what happened in Crossbell before Erebonia took over, and it features Lloyd and co. I would highly recommend you play those if you intend to venture forth in this series. Obviously, the graphics won't be as good as CS4, but that's what you get for skipping ahead. X)
Note that Reverie, which comes out this summer, will include transfer bonuses from Azure and CS4.