You will not be able to rent a car until you get your residence permit & Qatari drivers license. Cab are not expensive. avg 8USD-10USD
Depends where you are from and it may make it a bit easier if you also bring with you an International Driving License
You will be required to use the Bank of Qatar. Why? Because you will not have a RP to open a bank account with any other bank. Once you have your RP, then you can bank with the other local banks.
Simply open an account with IBQ on day 1 induction when you arrive. They have an office in the HR department of Qatar Airways.
Ref accomodation. Wait until you get here before worrying about it. Use what is provided and have a good look around. This being the best reason to hire a car