Hey mate, welcome to the club,
The 156 is a fantastic car and you certainly won't be disappointed with it.
What I can't stress enough though is this: Make sure you buy one that has had a recent cam belt / tensioner change done on it, and water pump done too if you can find one. As these are a necessity otherwise you'll probably have to get it done straight away, depending on mileage of course.
Alfa Romeo also tend to have a bad rep with electrics (Or so I heard!) so make sure you check everything works, from mirrors to windows etc. I have owned my 156 V6 for a few weeks now and everything is spot on, bloody love the car to bit's!
Good luck bud, and if you have any more specific questions just ask us in the Technical page for the 156 as we would be happy to help.
Take it steady,