Sturaro needs to work on his composure on the ball, he'll be a top player in his category if he does. Gattuso was not a strong technical player but he generally knew when and how to release the ball to better footballers. Sturaro still dawdles on the ball too much for my liking, he needs to see what is around him.
The Vidal comparison is interesting because there are some similarities. For CM players they are both sharp in front of goal, they both have very good defensive skills (Vidal is the best in the world for this), both have a degree of fearlessness to their games, and also there were many times where Vidal would would give the ball away and then win it back himself, which Sturaro tends to do. Where Vidal is much better is his awareness and reading of the game.
I don't think you can replace Vidal like-for-like because he is a fairly unique player in the last 15 or so years, but for what will amount to €11m he is on the right track.