I don't know about Duncan, but I've never been a fan of LaRussa. Yes, he's had some success in the past -- but he's also had some disappointing results that rival what the Yankees have gone through with Torre in the last few years (those Oakland teams of the late 1980s were a perfect case in point).
In addition to that, I would never trust a guy who spent most of his career managing teams in which so many key players were involved in steroid controversies.
Dave Eiland is the name I hear mentioned often as the new pitching coach. I think he's worked with the young pitchers in the past.
As far as pitching coaches go, the legendary Leo Mazzone has just been replaced in Baltimore. Don't be surprised if he ends up in New York next season.
I know Mazzone was let go, and I've seen his name mentioned and he is highly regarded, but Dave Eiland is the name I've seen that is given the best shot. I believe he has worked succesfully with the young pitchers in the minors who are now in or own their way to the Bronx.
Interestingly, Bowa is moving to Seattle as 3rd base coach, and Mel Stottlemyre is going there as well as the pitching coach.