Before you buy, check that each oil change has been done within the stipulated mileage of the previous one. Just one oil change over that limit should be cause for concern. For a diesel, the time is immaterial. You could wait 15 years before changing the oil and no damage would result, but if you were to wait 15000 miles that would be a bad idea! This is because the combustion products from a diesel (essentially soot) are different and not corrosive to metals compared to those from a petrol engine.
With the right oils, a diesel should be good for many miles, and should easily outlast the car. 112k miles will be only the beginning for it. I use Millers XFD fully-synthetic oil myself in my GT JTD nowadays, but there are others as good on the market. XFD is diesel-specific, and is far better for the engine than oils meant for petrol engines. Avoid the latter if you can, and insist on a fully-synthetic version of the former.
If you do a low mileage, then theoretically you can leave the oil change until the mileage is up, and do all the other time-based things (brake fluid changes, cam belt, water pump etc) round it. For a high-mileage car such as the one you have been looking at, that might be the right approach if you don't reach the magic mileage within a year.
Cheers and good luck
Sorry, but I disagree with some of what you are saying.
I don't see why extra oil and filter changes are "cause for concern", there are a lot of AO's on here that routinely change their oil twice a year.
Although most oils nowadays are pretty good, they also contain additives to make it thinner whilst the engine is cold, (the 0, 5, 10 at the start of the oil number/grade) and these additives break down. The lower the number (eg, 0) the more additives it will have inside it, and hence those additives will degrade and your oil will require changing.
I have never heard of any problems with extra oil changes, however extra changes at the start of the engines life, will just means it will take longer for the engine to wear in.
I would rather have an alfa that had twice the required oil changes over one that had half the required oil changes, in a heart beat.