Hi Arundhuti,
Bhutan is a great choice for travel destination any time of the year. I went in February 2014 and it was one of the most memorable trips of my life. In 7 days you can easily cover Thimpu (2-3 days), Paro (2-3 days) and Punakha (1 day) , do the tiger's nest trekking which is awesome (1 or half day for that), chelala pass and dochula pass (will be on your way from one city to another). You will find all your answers here:-