Last year my brother had Matt Stafford as his backup and tried for weeks to trade him before eventually giving up. It's hard to trade QBs these days unless he happens to be one of the big three (Manning, Brees, Rodgers).
Good TE, good K, good D/ST. Good QB.
Other than Cobb and Murray, your RB/WR group is pretty weak. Sanders and Bush are okay. Benjamin is okay as a late round lottery ticket. Can't say I like any of the others and I doubt I would commit a roster spot for any of them, personally.
I like Murray and Bush but talk about injury risk. You need to have way better and way safer options behind them. The odds of them both staying healthy all year is really unlikely.
I would ditch Newton, Fleener, Michael (since you don't have Marshawn). Good luck trading Newton, it won't be easy. That he lasted until the 10th round should give you an idea of his trade value. Stafford doesn't hit the bye until week 9, so if you hold Newton it's only as trade bait, and I doubt he'd get you much if anything. If anyone is smart enough to trade for Newton, they would have drafted him before you did.
Maybe you could keep Newton and platoon him with Stafford? I'm guessing Stafford has some fairly big home/road splits since he plays in a dome.