I think you'll be ok with your QB's, you can play the match-up week to week....however, you're right on about your WRs. A lot of things hinge on what happens with Marshall. Even if he does play for Denver, he's not gonna have a lot of time to get used to Orton (and who knows if he'll start). If he does get traded, it looks like the Jets, and a rookie QB is usually bad news. If he doesn't get traded, you're still in trouble because you handcuffed your starting wide-outs, which here, I think is a bad thing, especially if you want to start both of them.
Forte & Portis will do great, but then you have Lynch in the flex who is sitting out the first few games of the season due to suspension. After that, it's all down hill. None of your other backs will put up numbers.
You might want to trade one of your QB's or Defenses'. Both the Chargers & Titans should have solid season. I think you would probably be able to get a descent WR....but I would wait to pull the trigger once the whole Marshall thing cools off.