Agree cut off rootstock sprouts. Question is whether to thin down the scion sprouts. My concern is tree vigor going into fall so as to avoid another freeze back next winter. I'd probably risk it and cut back to the best shoot. But then don't push the tree with either water or fertilizer and no more pruning. Try to settle the tree down by September. The hope is it quits growing in early fall so as to harden off on time.