What a lovely gift. Those blooms should dry on the plant and last for months. Once they turn brown you can cut them off and just keep the soil moist not wet. The yellow leaves indicate lack of fertilizer or too much water or perhaps too much sun? Feed with Osmocote Plus slow release fertilizer and make sure the pot drains and does not dry out. Hydrangeas like morning sun and afternoon shade. You can also transplant this hydrangea into the ground in the fall and it should grow into a large shrub. Watch this video for more information. Keep growing, Marianne Binetti