Nice quince, as Owen said, they need a lot of water, barely damp is too dry, they drop leaves to balance moisture. As the sun gets hotter, give afternoon shade to keep the leaves. I too would recommend a larger pot for a couple years. A late summer repot is a good time to make the move. Dont do pruning this year, let it get bigger and well established. then you can begin hard pruning after 2 years of letting it grow out. The best smaller size bonsai do spend some time as bigger shrubs before being reduced to size.
