5.5 quarts with the OEM "shorty" filter, a full 6 quarts if you use an FL-1A equivalent filter (which I do on my 4.0s, and strongly recommend- I use the Pure One PL30001.)
The 4.0 is not a picky eater when it comes to oil, so it will probably be happy with whatever you put in it. The factory spec is 5w30 but a huge number of Jeepers, myself included, get great results (both scientific such as used oil analyses, and subjective such as engine "sound and feel") using 40-weight diesel engine oils. My preference there is Rotella T6 5w40, and I run it to at least 6000 miles (usually more like 7000 to 9000) with the large sized P1 oil filter.
The 4.0 talks a lot- its a noisy engine. You can hear lifter tick and piston slap routinely, but its not a problem. They just never gave it any sound-deadening valve cover or oil pan.
Your 2002 should be past the time when cylinder head cracking was more common than it should have been (2000 through mid-year 2001) so no worries there. You pretty much have a 300,000+ mile engine if you give it decent maintenance. 200k if you abuse the heck out of it.
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