Welcome to the forum mate... A good choice of car and no doubt, well looked after by the previous owner... The tip that we all give is: Buy an Alfa from a fellow enthusiast who knows how to look after the car
You have done exactly just that, so you are off to a good start
Alfa's are reliable cars, as reliable as any other marque as long as you keep on top of them.
Where they differ is that they require an owner's input like regular checks of fluids and servicing. Don't wait until the service is due, set yourself a lower target like for example every six month or six thousand mile for an oil and fuel filter change and every 12 month or twelve thousand miles for the air filter and you will have no issues.
JTD's have problems with EGR valves and MAP sensors due to carbon build up in the manifold.... This can be avoided by regular fuel filter changes and stopping yourself doing short journeys to the shops all the time...
They are mile muncher's and are more than happy to get on the motorway and cruise along all day long
So once a week, get it on a motorway for 10-15 mile at least and stick to a steady speed so the carbon soot has a chance to burn off.... You will never have any hassle out of the above then
156 have really well sorted dual wishbone suspension that offer's excellent handling, however..... because of its relative complexity, they tend to wear quicker than single wishbone shod cars...
Any noise, creak or knock... Get it inspected by a local Alfa independent specialist and get it diagnosed... Don't leave it or you will end up replacing more than you bargained for as pressure and excess play is put on other parts that were fine in the first place.
One last tip that I pass on to the less mechanically minded new owners that often pays dividends....
MOT's can be used as a diagnostic tool to your car's general health... Why wait full year?
Get an MOT test every six month and you will find that your yearly bill for worn items will greatly reduce as you catch them affecting other parts in time.... Doing general oil and filter changes yourself instead will more than cover the extra cost of a six monthly MOT..