I am sure more detailed replies will follow but please see the google map for your intended route, you can skip Hyderabad unless you want to go to al manzar and order palla or see the Kotri barrage, you can also stop over at sukkur and do the same infact added advantage would be dates in sukkur.
Other then that you can stop over at Naukot and make a side trip to Umerkot as well, to proceed to Nagar you will need a 4x4 from Mithi onwards, can be rented as well from Mirpurkhas, winters are good to watch migratory birds in wetlands or lakes such as kalri or Haleji but again these are side trips from your main destinations.
As far as my knowledge is limited no permission is required to visit Nagar, gulf rulers might be there for hunting and cant say for sure what it would mean to your trip if you happen to be on their collision course.
Lahore, Pakistan to Nagarparkar, Pakistan - Google Maps
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