Welcome to the 4x4 scene!
What rigs do your inlaws drive?
If they are the ones you will be wheelin' with, get a rig somewhat similar to theirs. If they are running 38's, you may not want to get a rig that will never handle 38's.
I was SOOO happy to finally get a cherokee when I got mine. I did a 2-3" lift and 30's and rear locker and was really happy with what it could do. However, nearly everyone in my club had migrated to 35's or bigger (this was back in '95) and I was beating the he!! out of my XJ to keep up with them...so I sold it and bought a platform that would easily handle bigger axles and tires, and something (else) I always wanted anyway (a scrambler).
So, like I said, if they all drive mild rigs with 33-35" tires, an XJ will be perfect and I'd take Bart's and XJEEPER's advice and also throw in a rear lockright and the most aggressive 31" tires you can live with. The advice about having it NOT be your daily driver is good. Having it available to daily drive is better.
If the inlaws all drive rigs with 37"+ tires, start with a platform that you can build up. I'm not saying you can't put 35's on a XJ...it happens all the time...before the owner moves on cuz the unibody gives out. OTOH, Chevy 1-ton axles on a sprungover YJ is a pretty cheap recipe for bulletproof go anywhere big tire fun, and you can start out with 31's and a swaybar disconnect while you learn to drive it.