I hope u will hv google map in ur phone download offline map of ur trip so u will not hv any problem.
Take N5 throughout karachi,use motorway where ever u find it, for breakfast lunch make royal taj restaurant ur stop, they hv chain of restaurants and patrol pumps.
I drove my car last month from karachi to bahawalpur in one go, but i did well rest before driving and used to stop after every three to four hours, for duration of 5 to ten min to rest my self