At first glance, you have to improve LG and LB (the position Moats and Bradham play). After that, it will be interesting to see what happens with Byrd, Leonhard and Searcy are fine players but not starters.
Regarding QB, I can see Cutler and Schaub, maybe, being available. I would not be opposed to bring one in. Pears is upgradable but Hairston will be back next season.
Marrone needs to have a serious chat with his friend Crossman, make him the HC consultant and bring a real ST coach.