The first part of his plan was finding a way to make sure Tom would be focussed on Hogwarts, the draw of Harry wasn't enough so Albus had searched for something the former dark lord would desire. The search had been made simpler when Nicholas had come to him with his desire to see the stone destroyed and his fears of something stalking him, it hadn't taken long for Albus to connect who it was hunting the Famels. So bringing the stone to Hogwarts was the perfect way to focus Toms attention.