Pats gave Bolden $2 mil guaranteed in the off-season so I'll be surprised if he doesn't make the team. If there is an odd-man out, it's probably Burkhead. But I also wouldn't be shocked if they kept all six RBs.
When you include special teams, I don't think it's a stretch for them to find roles for all six RBs on gameday. Michel/Harris can split up being primary ball-carriers. White/Burkhead can split up passing downs. Develin does his thing at FB. Bolden and Burkhead both play special teams. Plus, injuries are likely to happen at some point. Keeping all six doesn't seem unreasonable to me.
Brady turns 42 tomorrow and his stats declined pretty much across the board last season. Gronk is probably not coming back, at least not this season. Outside of Edelman, James White is basically the only proven, reliable pass catcher on the team (unless you want to include Dorsett, which seems like a stretch). And they can only throw the ball to Edelman so many times, or they'll risk running him into the ground.
In other words, don't be shocked if they run the ball a lot more than they have in the past this season, and save Brady for when they really need him. There's also been some indications during camp that they'll throw to the backs more often this season, which makes sense given their relative weaknesses at WR and TE, compared to the depth they have at RB.