Valverde rotates a lot, but no Rakitic for me will definitely play a lot more than Vidal does. Vidal is not better than Rakitic and especially not for Barcelona.
It won't. Busquets is a very underrated player, Vidal cannot play that #6 role as consistently and effectively as Busquets does. Bookmark this post, and we'll see at the end of the season. I'd be shocked if I was wrong about this.
Vidal's only chance of being a regular starter is if Coutinho is moved to the front three, meaning there will be a free spot alongside Rakitic and Busquets. Otherwise like Paulinho he will be a rotation option.
Also, Valverde is a little more flexible tactically, Barca play 442 at times as well, with Suarez and Messi the front two.