I did this road trip from Karachi in Dec 2016. You can take a look on some pictures I took here: https://imgur.com/a/dxqAP
I would suggest you to leave early morning from Karachi, ideally after Fajr. You will have plenty of time to make stops at Chandragup volcanoes, Hingol National Park (Hinglaj mata mandir), Kund Malir beach, Princess of hope, Ormara beach and still reach Gwadar before 9pm.
We stayed at Royal Resort in Gwadar and it was a good hotel.
You won't find company operated petrol pumps on Makran Coastal Highway after Winder. You can get Irani petrol from local shops at Kund Malir beach and at Ormara after that. Shell, Total, Haskol, PSO none of them have any gas station on Coastal highway and in Gwadar city as well.
There is not much to enjoy in Gwadar city except the beach and the view from top of the mountain. So make sure you enjoy the journey as it offers some great landscapes of Balochistan.