Seattle's defense is good, but I expect them to regress. They'll still be a top squad defense, but I don't think they can keep up the high level of play last year. Remember the 2011 Niners' defense? Last year's defense was still good, but not at the level it was in 2011. I expect kind of the same from Seattle.
Your secondary is good, but I'm curious as to how well Sherman and Browner will play this year now that they aren't taking PEDs. I'm hoping the refs will be watching them more closely as well, since they mug receivers up and down the field. I'm a huge fan of ET though, he's the only Seattle player I'd want on the Niners.
I think a lot of people are overlooking the Rams. They tied and won one against us, and took one away from you as well, including almost sweeping the series in the season finale. Fisher is a good coach, and the defense shows it. I don't think Tavon Austin is going to be a "game breaker", but the addition of more weapons for Bradford and the continuance of the same offensive system for the first time in his career can only help him improve. NFC West is the best division in football right now, and it's going to be a dog fight to win it this season.