audis are well built... if you look on ebay/autotrader you'll find plenty with 150k+ so they don't have many problems.

is it petrol or diesel??

wat happened to the alfa he was looking at or was that a different friend?

Nothing wrong with that millage as long as service history is present and it reflects the price, the Audi is renown for build quality most engines nower days are good for big miles but I think people loose site that its not just the engine, a mate of mine owns a 52 plate Vectra high miles but the money he has spent on it is nobodies business I convinced it was a cab hence well worn all over but engine wise not a problem

Don't Audis suffer from the usual German car problem of stalling if doing less that 80, or if its more than 1 meter away from the next car in front?

They are well built, but I would want to see full service history at that milage, or I would walk away. Personally I would look for something with lower milage though as the gearbox and engine might be ok, but the brakes, suspension, steering components, driveshafts etc etc will still have seen 150k. Mind you, saying that I once spent 350 quid on a Toyota Carina mk2 with 155k on it. Had a dodgy CV joint which I knew about when buying and replaced it straight away, but other than that owned it for a year, and never had a single problem with it.