Thanks for your comments and advice.

The company have arranged limo to collect me and my son from the airport and to take us to the hotel. I was not sure if I would need to tip the driver or not.

I think that I will just use my card to withdraw cash from my UK bank account when I first get to Doha so that I have some cash to use for small purchases and I will pay for larger purchases with my card.

Thanks again for your help.