Check all your fluids every week, keep to a routine and monitor the fluid consumption, oil usage changes with driving style, for instance you may use more oil on a high speed run if the car is normally just poodled about, thats why figures given can only be a guide. 1 litre of oil per 1000 miles is acceptable, as the twin spark engines can really drink it when bedding in, it is important to check it regularly. This can also highlight problems before they get too serious, for instance if the coolant needs regular topping up, the system may have a leak which can be easily fixed. If left it could mean a headgasket failure on the way.
Oh yes, those oil consumption figures do mean a ts engine can empty its sump in less than 5000 m iles, so keep an eye on it! Finally use Selenia 20k in your Alfa, after all its what Alfa recommend.