Dec-Jan is a best season to discover South;
From Isb you can go to Khi via Indus Highway which is around 1260kms.
Khi to Jiwani is 710kms, major points are Chandragupt Mudvents, Sapat, Kund, Ras Malan Beach will take a whole day. All depends on you to stay or camp at Sapat or Kund Malir.
Ormara and Pasni beach can be seen from Makran Coastal Highway, Gwadar and Jiwani can be done in a single day and better stay at Gwadar.
Don't forget to visit Pak-Iran border via Pak/Iran Friendship Highway, 30kms from Gwadar.
Whole round trip would be around 4200-4500kms, so 280-320kms per day is adviseable.