I like your idea, but I agree with Leemo that it may be too much dedicated to one positional grouping. There's no need to move Dennard in the slot in my opinion. He proved to be just fine in his rookie year and could make a nice leap up in his second.
I wouldn't see any scenario where Belichick would fail to take advantage of having an adequate starter on a cheap rookie deal, that wouldn't make much sense to me. You are also not factoring in Arrington in the slot, and by all accounts the team wants him back. He should be pretty cheap, around 2-3 million at the most.
I also think that when it comes down to it we won't see Talib resign here unless it's for a shorter term deal and/or reasonable money. There are just way too many options as you have noted. He isn't as much as a priority as some are acting like, and poses an insane injury risk. The guy's had the same 2 injuries for three consecutive seasons (IR in 2010 and 2011), and in all three seasons he's missed significant time at the end of the year. I don't see how we can count on that, and it seems to be way too much of a pattern, particularly as the season progresses and winds down.
I'm sure BB wants him back, but whether or not Talib agrees to the money and terms that BB wants him back on is an entirely different question. If it's not him them you could add in any number of other options which may be cheaper anyway.
I agree entirely with your proposal to add depth to the entire secondary, I just think we'd need to pull one of the higher priced guys out and replace him with Arrington for a more reasonable solution that would allow us to address all of the other areas of concern.
My note on moving Dennard to the slot is more about what we expect his availability to be. We might need to replace him outside for a period of time which we don't know yet. If the market is flooded I'd like to see us strike now.
I would also prefer another CB over Talib, but, there are a few signs pointing to us wanting him above anyone else at the moment so that's the reason I went with him, that decision was more about what I THINK will happen while the rest of it is what I WANT to happen.
I also like Arrington in the slot quite a bit but I see some team over paying for his services and using him as a #2, something we hope he wouldn't be again here as he isn't suited for it. He has stated that he's drawn interest during the past few days.
edit: I'm also projecting the offense to return almost entirely intact with the exception of Vollmer.
Welker resigned, retain Lloyd (lets face it, it'd be extremely difficult to replace 900+ yards for 4m). Gronk and AH getting healthy over the offseason. Ballard should be fully recovered by now, Line stays mostly intact, both guard spots getting healthy. RB is hardly a priority, Vereen looked ready to take over Woodhead's role in the offense late last season, Demps could factor in at returner.
Should be cheap options to add depth at WR, reports we want Stallworth back, could throw an offer at D. Alexander, D. Nelson is out there. Branch is always willing. Draft is deep at DL and WR.
I see this free agency period as one where either the secondary or pass rush needs to be addressed in a big way, and the pass rush options aren't the most ideal anymore. WR has no real mid-level options, its either top talent or bottom talent.
I'm not seeing many other areas that can be addressed in any significant way, especially offense, in free agency. The draft is a much better spot for DL/WR help this year than free agency will be.