Toruu
Become an international duelist. Fleur was one and he could know her. With her assassin's coldness he would do quite well. The most interesting thing is that the duelists probably have separate training from Hogwarts. After all at hogwarts, dueling is only done with lockhart and that was only one year. So the duelists probably have private trainers, it's more if the ministry sees that it's very good they can support it since it gives them some fame. And after a civil war it's the best. You can get some retired duelist to teach you, in exchange for giving your teacher some recognition. What's more, he could get Cedrella Black (his grandmother), knowing how dangerous the Blacks are, he could teach him. He dies after Sirius's departure so he has three years before he passes away. to pass the Black inheritance to him, since just like Cedrella dies after Sirius gets out of jail, (suspicious), and at the moment he is the Lord of the Black House, he can choose the heir he wants.