If you are looking at an earlier model the most important thing is to check the history and make sure the timing chains have been sorted. Earlier ones had plastic tensioners .If they go in mid flight it can do a lot of damage to engine.
Rust,rust and rust--no getting away from it i`m afraid. Check sills ,subframes ,floorpans and behind rear wheel arches. Good news is that it can all be sorted.
Owning one of these is great but it will cost you. If you are scared of that prospect then my advice is look elsewhere. Harsh but true. BUT its a fantastic car.
I splashed on an XKR a couple of years ago and even though it costs a few bob now and again the novelty value has still not worn off. Good luck