Should I make this fantasy Football tradE?

You do it and you don't think twice about it. Portis is an old 29; a lot of carries on those legs. And considering you already have Manning losing Schaub is not a big deal. Turner is still a 1st round player, and you can't hold too much against him for struggling at Pittsburgh. And young isn't receiving much, but will be an adequate fill in for Peyton on his bye. You are getting excellent value without hurting your starting lineup at all.