3/8 ratchet for the level plug. Personally I'd use 75/140 synthetic in both ends given the reliability of Jeep axles.
Jeep's schedule says you should change the oil at least every 30K miles, I would do it more frequently, they have a terrifying appetite for bearings, and once they're noisy it's too late to do anything other than rebuild the axle. The 75/140 fully synthetic is reccomended by Jeep for the rear for towing and hard use anyway. use it all the time, it's pricey, but not as pricey as an axle rebuild.
From the description, it looks like you may be able to use this without the additive, as it's formulated for limited slip diffs. Call them and ask the question.