Fuel for my 525i is usually about $55 for 45L of petrol (I always fill up on Tuesday afternoon) -- this is Unleaded 95 octane.

I doubt the 525i is considerably worse than the 520i in terms of economy. The E34 is not a light car, I think the 520i would be struggling a bit more trying to shift all that weight.

If you're going for a 520i, the manual is probably a better choice -- a 520iA would be quite sluggish. Don't be surprised if you open the bonnet of a 520i and see all this empty space

There are a few E34 replacement parts that pop up on eBay Australia from time to time -- especially clear lenses. If you like this look, you could pick up a pair or two to maintain the more modern look. Get a pair of good rims and maybe even lower it and you would have a fairly respectable looking car -- except for that 520i badge on the back just kidding.

The E34 is a good car -- it's my first car and I'm a 2nd year graduate, so it wasn't that long ago that I finished my studies. They're quite solid and usually only break down if they haven't been well maintained.