I agree with all of UtterBlitz's points - very good summarization.
If
Torry Holt is your only blue-chip WR, I'd definitely keep him. Even if he is slowing down, he's still a lock to get you 1100 yards and 6 TDs, plus his game-to-game numbers are normally very consistent. His knee worries me, and he might be more of a possession receiver now, but there are currently no other dependable options at WR so he should get plenty of looks from Bulger.
As far as those RBs go, I think Willis McGahee and Clinton Portis are your best options. Ryan Grant may have been a one-year wonder benefitting from the long-ball threat that Favre brought to the table - hell, the entire Green Bay team might've been a fluke last season. While they have a solid, young squad, I could easily see them going 5-11 without Favre at the helm.
McGahee should flourish under Cam Cameron's system (see: L.T., Ronnie Brown pre-injury). While he didn't have eye-popping numbers last year, he was still the best player on their offense.
Portis might not be the most consistent player, but there are some weeks where he'll give you huge points. His injuries concern me, but since going to Washington, he's started 15/15, 16/16, 7/8, and 16/16 games. Other than the 2006 season (the only year I had him on my team, go figure) he has managed to stay on the field. Keep your eye on any news items that might clue you in as to how Jim Zorn wants to distribute carries between he and Ladell Betts.
Both Portis and McGahee are also entering their prime, as they will both turn 27 years old this autumn. Grant, while new to the scene, is only one year younger. All three should see plenty of touches as they are in run-first schemes and have no quarterbacks that can really carry the offense.
If you have more confidence in Grant than I do, factoring in his younger age and fresh legs, it's a toss-up. But personally, I'd go with Manning, McGahee, Portis, and Holt as my keepers.