What I would do is level the trailer and then measure from the bottom edge of the coupler to the ground. Then measure from the top of the opening in the receiver on your WK to the ground. The difference is about what the drop of the hitch needs to be. The top of the opening of the receiver on my WK was about 21" above the ground and the hitch height of the scout trailer was about 13" so that gave me an 8" drop for it to be level. I think you're going to need more than 3" for sure. My boat trailer has a higher hitch than this scout trailer did and it tows level with a 4". I have a 2", 4", 6" and 8" drop hitches. You can just get an adjustable one which might be more convenient but get a good one that does not rattle.
As far as towing with WK Hemi vs Diesel, well, unless you are right at the limit and tow in the mountains, the Hemi pulls like a freight train. I tow an '88 Four Winns 21' bowrider that is probably a bit over 4,000 and it hardly notices it back there. My neighborhood has many steep hills and I have had no issues pulling the boat up steep hills. I would not even think of trading for a diesel unless I drove a lot more than I do. Love the Hemi and Chrysler electronic 5 speed. Light years ahead of the old stuff.
Air bag install, I have not done it on my WK yet but I did put them in my ZJ and it was pretty easy. Running the air lines is the hardest part. I did remove the springs on the ZJ but that was easy too.
Your tongue weight sounds OK but measure it to be sure. Even with a light trailer your tongue weight has to be right or it can sway. Too little tongue weight, too high hitch in front and underinflated tires can make it sway. Tongue weight should be between 5-10% of the total weight of the trailer. If its 2000 lbs then 175-200 is OK.
As an example, I would up towing the trailer above because the assistant scoutmaster's Suburban's trans cooler started leaking. I followed them on the way to scout camp and I noticed the trailer was definitely swaying, not uncontrollable but still I did not like what I saw. Their hitch was too high in front and the tire press was low. For the return trip, I got the tire press right and had the right drop and it towed perfect at highway speeds, despite the fact that my WK is much shorter than the Suburban.
2007 WK Limited Hemi QDII
1998 ZJ Laredo 4.0 Selectrac