Surface cracks don't generally harm the performance of the bat, especially if they are near enough in the centre of the blade. As an opening bat I generally take a little longer to make sure my bat is knocked in, and also apply the scuff sheet to prevent seam damage from the new ball, as well as trying to minimise surface cracks as much as possible. I'd use throwdowns with some good quality older cricket balls as a way of introducing the bat to strokeplay, and it's also a good way to get used to the feel of the bat, the sweet spot, etc, before you use in a game.