Well you need to focus on popular places where there are people (visitors) for the whole year and not just in a particular season. Since Murree already has lots and lots of shops I won't recommend it. Kashmir is vast and has proper cities like Mirpur, Kotli, Muzaffarabad etc but I think you want to open shop in holiday destinations which are frequented by travelers. Abbotabad is also a proper city where there is local population and less visitors.
I think after Murree, the place where most people visit for vacationing is Nathiagali - where I didn't find many shops comparatively even though there are quite a few good hotels there. So do check it out for a business opportunity there.