My '97 I6 has been surprisingly reliable. I haven't had any major issues with it, mostly just wear and tear items. I'm just about to hit 148k, btw. Biggest things I've had to do is replace the front CV joints at 112k, and the rear axle seals and bearings at 146k. I did them myslef, it wasn't too hard.
A thing to look out for is the VC in the 249 (Quadra-Trac) t-case, but a 6 cyl will most likely have the 242 Selec-Trac case, which is very reliable and shouldn't have any issues.
Check the AC, chance are it won't work, mine hasn't in years. IMO AC has never been the strong suit of any Chrysler vehicle.
And no timing belt, the 4.0 runs a chain. You'll probably never have to replace it.
Also check the rockers and bottoms of the doors for rust or rot, it seems like that's where these corrosion problems start. If It's got plastic of the rockers and you can't see them, I'd make sure to check the doors....if those are going, chances are the rockers are too. Mine is starting to go in those places, what you want to do is open the doors and look at the bottom inside edge of it, that's where it rots.
I can't really think of any other major issues you'll have, the 6 cyl is pretty reliable.
Oh, and check the parking brake, chances are that don't work either. These things are notorious for that.
And on these, it's really not so much the mileage as how it's been taken care of. You can get 200k easy out of these if you take care of them, hopefully your previous owner has.
The nice thing aobut Jeeps is that if you have any automotive knowledge, or even the willingess to try and learn, they're relatively easy to work on. I've owned mine since '01, and it's only been in the shop 3 times. For the most part I try to do everything myself.