I don't think 4 days Cuzco, including MP, is too much. You need at least 1 day for the city of Cuzco, which is best to be seen walking. Don't forget that at this altitude, you need more time to walk around and don't forget that after your day tour to MP you will certainly be tired the next day. If you do this from Cuzco, be prepared to leave around 05:00 am and come back around 09:00 pm. You also need time to get your MP tickets, best to do so in Cuzco while you are there.
Pisac market is very colorful and once there, I suggest to visit Pisac ruins. By the way there is a good hotel in Pisac (Royal Inca) at little bit ouside the village, but within walking distance to market and ruins. Calculate a full day for Pisac (market and ruins). There is also a good hotel just beside the train station in Ollantaytambo from where the trains to MP leave, this saves you the 60-120 minutes ride Cuzco-Ollanta in early morning or late evening. I would consider going to Ollanta after Pisac, instead of going back to Cuzco.
If you are worried about altitude sickness, start out with sacred valley, this is at lower altitudes than Cuzco itself.