Getting a Q2 fitted will cost £600-£700 from a good indie, and is well worth doing on the V6 GT, so budget that for the difference between one with and one without. Personally I'd be very wary of a five year old car that's only done 14k miles, whatever the service history might say. It's either done lots of short journeys that haven't warmed up the engine properly, or it's only done one or two long journeys a year. Either way, the engine's not been treated well. The motor trade is still obsessed with low mileage, and charges a significant premium for it, but proper servicing, on schedule and well documented, is far more important.
The official cambelt replacement interval for the V6 in the GT is five years of 72k, whichever comes first. Most indies recommend leaving it no longer than 4 years or 60k. You need to get the water pump changed at the same time - it was originally fitted with a plastic impeller pump, which had the habit of disintegrating and seizing up the pump, throwing the cambelt with upwards of £4500 of damage done. All tensioners and pulleys need to be replaced at the same time as the belt, and it's quite a technical job on the V6, so best left to someone with lots of Alfa experience.
One other little thing regarding the V6 GT. If it was first registered before 26 March 2006, it will cost you £235 a year to tax. After that date it's £435.
All of which said, I've just upgraded my old diesel GT to an 05 plate V6 and don't regret it at all.