well, first its not a V4 but a straight 4, its a M43 engine with vanos. Its a very good engine, I dont know if its exacly the same has in here (Euro version)
It can take a good dose of tuning and boost I think. I dont know how much tuning material there is over there, specially for 4cylinder bmw engines. the only company I know of that you might check out is
http://www.metricmechanic.com/ Maybe Dinan might have some stuff too, but I think they work more on the 6cylinders and stuff.
The rest of the car is standart E46 - great quality, reliablity, great chassis with great handling. Sum-up: Great car.
I think you´re getting a sweet deal.