Well I have a 1.8T and I love it. My mate has an A4 1.8T and I can pee all over him, so thats what I would get. The difference in insurance wasn't too much for me, but I'm 27 with 2 years ncd and 3 points.
I had a mk2 Astra GTE which also ran 150-160 BHP and they are both about as quick I think, and the astra was phenomenal (although I think torqueier??). Easily go 1.8T as if you can afford £1600 to insure your motor, you should manage a turbo. Then just go get it remapped.
If you can afford 1600 per year (insurance) then dont worry about cambelt. Just replace it and have piece of mind (about 40k for a change anyway, so multiples of that). Try to get one with good service history though. Good service history means the car was cared for, and hence probably no thrashed. Mine had full history with 1 owner, so every receipt is there.
As for the turbo needing replaced, well, its a shame when it happens, but its an excuse for a bigger one
