I don't quite buy into the Buttler at three hype because he is not good enough technically against the hard new ball - yes, he might come off occasionally but set against that chance you lose his genuine threat at the end of the innings. That said, I don't see why some flexibility is not shown - he should be coming in first available chance after the 34th so that he can play through the second powerplay.
On the wider hitter vs. accumulator debate, for me the ideal one day side would have two accumulators (one of whom can expand on that), four hitters and a wild card - one of these seven being an all rounder - as well as four front line bowler whose batting skills are of limited relevance. In terms of accumulators, I think Bell and Root (the latter because he can expand on that and also bowl some useful spin), my hitters would four from be Morgan, Pietersen, Stokes, Bopara, Wright, Ballance and, for a name outside the box, Malan and Buttler is the wild card.