The biggest headaches will be electrical, and often the simplest problem will manifest in truly bizarre ways. Once you get past that down to the hard parts, you're going to fall in love with this truck. You'll need big wrenches for chassis and suspension work, and some odd sizes. Other tricks abound, such as the oil pan drain bolt being 1-1/8" (just the same as the lug nuts).
There's another very active discussion board, full of very knowledgeable people from all over the world. If you approach them sincerely they'll bend over backward to help:
About the auction, it's pretty important to run down the vehicle history by VIN at a Rover dealership to see how the truck has been maintained. You want to make sure she's had plenty of regular fluid changes, and as much documentation as possible. An ideal truck will have a fully complete Passport To Service. Fluid change neglect will show up in an all-alloy engine as premature (EXPENSIVE) wear. The auto trans is pretty much bullet-proof, as is the xfer case. If it has aftermarket lockers in the diffs then see if the owner put in upgraded axles. If not, walk away. If it's lifted, did the prior owner upgrade radius/trailing arms and drive shafts? Is it sagging on the offside aft corner? Also look for corrosion at the bottom aft corners of the rear seat door openings, there will be "a little" there, but better not be very much. Look at the big bolts underneath... has the long-term accumulated crud been cracked away from wrenches? If so, what was replaced?
I can't think of anything else, other than... if you've done a brake job on your Turbo Coupe, you're going to LOVE doing it on a Disco. It's like heaven with wrenches.
Get used to loving the truck early on, because when (not 'if') the nagging problems appear it's the affection alone that will keep her in the driveway. I had a thought this morning on my commute: owning an early Series Rover is like living with a child for years... they complain but they're easily dealt with using simple remedies. Owning a Disco is more like living with an adolescent for years... they have complaints which are more sophisticated and will take more effort to address... and will make you nuts dealing with them. Once dealt with, the good stuff comes pouring back again.
Good luck, -Bob