Hi there! welcome to H.CM.Forum!
Yes, you can exercise even after a stent
insertion. In fact, you should. The level of exercise you should do, depends on the condition you and your heart are. Initially, you can try a light walk for a minimum period of time, which does not cause you any discomfort. then, as your condition permits, increase the level and the time of exercise.
Swimming and cycling are also great options, but again do consult with your cardiologist. Yes, you can take the stairs in your home, depending on your tolerance level.
It took many years for the arteries of the heart to narrow down, causing a stent to be inserted. It will take time for the arteries to heal and recover. But also do remember, any form of exercise, can help in a faster recovery.