I don't think there's anything in particular that you have to do at 180,000km - it will depend on how much routine and preventative maintenance has been done and the particular condition of your car.
IMO, E30s are simple, robust and "modular" compared to the later cars, but they are an 80s design - there are a bunch of wear and replacement items and failure points which could be an issue at that sort of mileage.
Find a car you like owned by someone who can give an account of its maintenance and has owned it for a while, and then you will be in a better position to ask "what should I do to it". If you buy a 316 that's been used as a "beater" for years, you will potentially have a very long list of things to inspect/fix/replace!
For want of anything better, if you buy a 180k 316, definitely timing belt and valve clearances,(if not done according to the service schedule), engine oil and filter replacement, and replace the differential and gearbox oil immediately. Then drive it and see if any issues appear.
Xter wrote:Hey guys,
I see a lot of reactions, thanks a lot!
@rubber_duck89
I won't go for a touring hehe (no offence)
@Joketown
I don't believe you can make 45 MPG, not even 40. That 1 liter for 16km (sorry we use km here

)
@Neil_uk7
Well a 325 is not really a fuel saver. I 100% agree on pimped ones, I prefer a standard one, well, good rims are okay
@B7
Thanks for your advice but as you say, it takes time
@Saga
thank you for the link, I will defenitely take in consideration to buy one of those
So what if I buy one with 180.000 km, what do have you experienced what will have to be replaced first if it hasn't been done already?