I've got an '01 WJ V8 Limited 4WD. 150k on the clock.
There were two 4WD options on the WJ: Selectrac and Quadradrive with QuadratracII. Selectrac is a conventional 2WD, 4HI, N, 4LO. Only an option on lower end WJ's (Laredos) unless factory ordered. QD uses a full time 4HI with variloc axles front and rear (similar to LSD) and in the T-Case. 4LO locks the t-case.
So 1 is LSD F&R unless it is Selectrac (you described QD). The rear is a D44A (aluminum).
2 is most common problems are the blend door if it has dual zone climate control. $$ or alot of time to replace as the dash needs to be removed. Happens around 100k. Check the AC/Heat out of both sides and find out if it's already been done (good thing). Heated seats go bad often as well. Mostly, it's the luxury items on the thing that go bad.
3 Mine is a pig, get's about 12-15 with 31's, 4" lift, cat n back and intake.
I will tell you though, driving up in the mountains in the snow is a blast. It'll break loose if you push it but it holds the road better than anything else I've ever driven in inclement weather. HTH.