The XJ is great at 1 and 3, 2 not so much.
The 4.0L I6 / AW4 combo is pretty much bullet-proof and one of the best engine/trans combos around for reliability and ease of repairs and maintenance(The AX15 is good to but you stated you wanted an auto).
XJs are very easy to work on, there is a ton of aftermarket support and all kinds of "budget" upgrades using used parts from other vehicles.
For fuel economy the XJ (6-cyl, 4WD) was rated for 15 mpg city / 19 mpg hwy and that generally doesn't improve with age and any lift or oversized tires will reduce it even more. That being said any vehicle with equivalent capability won't do much better. For comparison a new Nissan Xtera (6-cyl 4WD) is rated at 15 mpg city / 20 mpg hwy, a JK Wrangler 4Dr. is rated at 16 mpg city / 20 mpg hwy, and a new Toyota 4-Runner (6-cyl, 4WD) is rated for 17 mpg city, 21 mpg hwy.
As years go all 91-99 XJs are good reliability wise. 97+ models have a nicer interior and updated (new grill, etc.) body style. 00-01s suffer from the 0331 head issue which is known to crack if overheated (Note: this affects all 00-01 4.0L I6s not just XJs).
If you live where they use road salt make sure to check for rust (this can be an issue on just about any older vehicle), especially underneath and in the floors. Surface rust is not a major issue but make sure to treat it with rust-inhibitor paint to keep it from getting worse. Holes can be a sign of major issues and if there is major rust that you can see there is likely more rust hiding where you can't see.