Engine is generally robust, has been in plenty of things and uses established (read ancient) technology. The 4.0 v8s had an issue with losing the Nikasil lining off the bores, and with timing chain tensioners. However this didn't affect 4.2's and iirc all R's are 4.2. Also, it's generally accepted that the ones that are still running will either have recon'd engines (usually under warranty) or the liners were good from the factory.
As for the car, papa '944 ran a 3.0v6 for years, (from 25k to around 140k) generally reliable thing, facelift cars (around 2002 and denoted by an electronic handbrake) are a significant improvement. Changes to electronics improved reliability and pre facelifts go through suspension components as consumables. Early ones did suffer rusty sills (under plastic covers), but not as badly as x-types. If I were buying one, I'd have the sill covers off first. As with a lot of Jags (past and present) random electrical problems are often caused by a battery that's still functioning but past its prime. Oh and check the battery, it's in the boot iirc and can rot out the floor if it leaks
Generally they have a reputation for being a handful in the wet and fuel consumption is around 14-27 for the v8 depending on the weight of your right foot.