Question 1: Can anyone advise if the 14,500 QAR accommodation allowance will cover the monthly rent for staying at the Beverly Hills Tower?

It's 21 for a three bedroom and 16 for a two bedroom. It's a nice place though.

Question 2: Can anyone advise if the Beverly Hills Tower is worth the rent or are there better value for money places to stay?

I'd wait and rent at the Zig Zag, it's in the same area, not in the congestion zone, and close to the Pearl. It'll probably be 14-16,000 for a fully furnished place.

Question 3: Can anyone advise if the 2,500 QAR travel allowance will cover a monthly vehicle lease? If yes, can anyone suggest a good vehicle leasing company?

Yes it will. 2,100 is the avg. You can try the usual, Hertz, Budget, Oscar, etc... or Al Mana have a special promotion for Hummer, Cadillacs etc.. (3 months for the price of 2)

Question 4: Give the above accommodation & vehicle lease costs can anyone advise a “typical” monthly expenditure for a single guy i.e. how much it would cost me a month to live in Doha (food, entertainment, etc)?
I have been advised that my salary would be paid into a local bank account. From this I will set up a transfer to pay monies back to the UK.

Check out http://www.iloveqatar.net and the Cost of Living section.

Question 5: Can anyone advise on the typical charges for monthly international transfers & also how much fluctuation there is in the QAR to sterling exchange rates.

Roughly fixed at 40-100 QR
There is a lot of fluctiation because QR is pegged to dollar.

1 pound hit 8 qr at one point, now it's 5.2 (which is great if you're in Qatar)

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Mr. Q's Blog - A Qatari's view on Qatar.