I used to own a model exactly the same as your prospective purchase. It was a fine car to drive, well-specced, and loads of space.
Well, you'll know these cars aren't very common, so I can only refer to my experience, and hope that other owners & ex-owners jump in to help out.
I sold mine after 2.5 years of ownership & 45,000 miles (it was a couple of years old when I bought it). In terms of mechanical reliability - I had no problems, but the big issue I had (which was why I sold it) was electrical faults; the car's battery would flatten if not driven every day (I had to resort to carrying a spare battery & jump leads in the boot), tyre sensor failures, rear doors would refuse to unlock, sat-nav would crash & fail to re-start. These problems could either not be found, or if so, no-one knew the car well enough to fix it.
Mine cost £10,000, and I only got £2,500 for it 2.5 years later...(a sore experience).
I have some experience of aftermarket warranties, and one I like is www.warrantywise.co.uk
, although you should be aware that the mileage will preclude/limit the coverage available on certain components.