I used my honda doing 100kms + a day for almost 6 months and nothing ever happened to it, it is a honda and it can handle it.

Hondas are built to last and most will make it past the 200k mark and even the 300k like mine, it also depends on previous drivers and how they drove it as im sure you'd know, the main problem in my eyes that you should be weary of is the transmission my gearbox just gave way and I got it fully rebuilt (although this was at 310 000kms) but they have been known to go well below this, make sure it has a log book and check its regular service dates.

As you are looking at 4th gens, clutches dont seem to last alot of 100k same with the timing belt, my break calipers and rotors have had some problems as well.

Mine has started to rust around the edges of the windows near the seals, not so much the sunroof for me but I have seen some pretty bad rust on some other preludes in that area and the area is prone to rusting for obvious reasons, rusting on the fenders below the rubber moulding is also common.

As for fuel economy I can easily get over 10ks to the litre depending on how im driving, I fill up once about every 1.5 weeks and thats driving everyday in urban areas, if your doing 120kms plus a day your basically looking at $20 a day on fuel.

Preludes are comfy to ride in if you like being close to the ground, I am over 6 foot and it can get quite cramped but overall im fine with it, if you are tall it might take some getting used to.