Call me old school ... but I could never understand leagues that have both a DEF and IDP's. As a fantasy purist, I say either/or ....
With 16 teams, I would grab ONE stud running back and then grab WR early and often... by the lineup, you MUST have 2 WR and probably 4... Serviceable RBs will be gone by round 2, so having a few stud wr in a very deep league would be to your benefit.