To my knowledge, Qatar does not allow the transfer of money from outside for individuals either through banks or money exchange companies. You can check this out through banks in your country or through any Western Union office in your country. You can bring in some cash when you are coming into the country.
As for how much cash you need to carry, it's not easy to answer. My own guess would be QR 1000.
You can PM me for further guidance on this matter.