Welcome to the Cafe!
Your team has a lot of potential, and as you'll often times find that potential can come with risk. With that being said, your team has the makeup to be competitive.
I agree that WR is your weakest position. Mike Williams is a low end WR1, and Santana Moss isn't a spectacular WR2. I'm worried about Plaxico Burress filling your flex slot, as well. Plaxico is a 34 year old wide receiver on a run first team. What WRs are available on your waiver wire? I doubt you will find someone who you are able to plug in right away to replace Burress, but I would look to roster a WR with a lot of upside who may break out.
Your have four solid RBs. Darren McFadden, Peyton Hillis, Marshawn Lynch, and Daniel Thomas should be able to keep your RB and RB/WR slots filled well. McFadden does come with an injury risk, but he is explosive enough to be a top 5 running back this year. There are some concerns about Hillis' workload, but he is just 25 years old. Even with his physical running style I don't think he is burnt out just yet. Lynch and Thomas are both slotted in to get a good share of carries in 2011.
I'm not too well versed in IDP, but it looks like you have several strong options. Patrick Willis is THE best player in IDP, so it can't hurt to have him on your roster. Willis, Tulloch, and Posluzny are all top 10 LBs who should be able to rack up solid numbers. Eric Berry is an elite DB option, and Peppers is a borderline top 5 DL. As far as I can tell, your defense is very solid.
You could use a little work at WR, but your team should be competitive. Good luck in 2011