1. Go for a Bank loan, preferably the bank where you get your salary transferred.
2. Minimum down payment for a car is 20% of the total value of the car.
3. There is no credit rating as in the US. If this is your first loan in Qatar and if you do not have a credit card from a Qatari Bank chances are that you would get a good interest rate. Try Commercial Bank because they have an interest rate starting from 2.69%.
4. I own a 2011 GMC Sierra and I love it. I am currently looking to sell it off and buy the 2014 GMC Sierra. Ford and Toyota have good cars but the after service sucks. No idea about the others. GMC has excellent after sales service.
5. If you need any other help, kindly lemme know. Would be glad to help a new expat.