There are two ways to reach quetta,
- Through Hub area enter to Baluchistan and through the highway reach to quetta. (Approx 700 km)
It will be better not to travel on this route because I think there is only 350 - 400 km road and rest is all under cnstuction since years. Uf you will try this route you will ruin your car.
- Reach to Sukkar, then enter baluchistan through Jakobabad and reach to quetta. (Approx 900 km)
And for your trip to quetta if you have Corolla then it will be very good, because this car is very common in Baluchistan and in case you face any problem atleast you can find spare parts and mechanics.
MY ADVISE:
Go from the Sukkar route, Till sukkar you will find good highway and after that somewhere bumpy and somewhere average highway. But be careful, your car should be very well maintained and take adequate quantity of water with you and every necessary thing for any emergency condition, because there are very dangerous turns and slopes so be very very careful, and car should be driven by a very professional driver in Baluchistan. Specially 100-125 km after sibbi are very dangerous. So be very well prepared.
It will be good to stay a night in Sukkar and next day continue your journey to quetta.
And in the last People are very very helpful and caring of baluchistan so be very polite with them, if you will give them respect they will respect you more than you expect, and waer local national dress(Shalwar Qameez), if you will waer PAnt Shirt they will consider that you are an ALIEN. 
