from what I have read, the gasser Libbys get about what your 4.0 gets, my CRD is getting mid 20s with mixed driving, I'm hoping it gets a little better with more miles
Liberty owner here!, the KJ is a great daily driver. Its comfy with nice tight handling and lots of neat features, and an adult can even sit in the back seat. BTW I'm not a woman , but I do have 3 kids so I need to have room for them once in a while. I'm very happy with my little Libby! I plan on some mods soon but its still fairly new and I need to break it in a little more. They are IFS as you know and they take some work to find the right combo of lift and tires from what I understand, but maybe that would help keep it a daily driver instead of a project(part of the reason I bought mine :-D ).
Also, that looks like a good deal at that car lot but the 3.7 is not great on gas.