I would suggest that since car is of low height cannot ply on Babusar top road u may not use that road. Ten to 15 km road is bumpy and un mettled. U may go to islamabad, and take Karakuram highway at Hawelian, abbot abad, Shinkyari, Thakot and Bisham Chilas and Gilgit. Hotel here are not good. Take rest in Gilgit. Then go to Hunza. Stay there overnigh. Good hotel u can find. Then go ealy in the morning to Khunjrab. Ask many travelleors and plan then and there.