I've done two WJ Big Brakes, and converted one to 5 on 5. I did that as some WJ rims came up. Originally I ran some 15 inch Canons with spacers.
My present setup I used 2000 XJ 16 inch aluminum rims. 5 on 4.5. I think they are call the unlimited. I did try some steel rims, but the binded on the caliper. I went with NAPA Reactive and Adaptive pads and rotors. I think you might want to look at Black Magic pads.
Also, look at Cobra Marty's page. He has info on using the Mustang rotors and Dakota calipers. This is a `13 in rotor, so probably a 17 inch aluminum rim. I am looking into using another rotor.
OK, I have used a 07-08 Liberty rotor for my WJ 4.5 on 5 setups. It works good, but you lose about 1/16 on the OD. On a discussion on the Comanche Club board, I started to look at other rotors and caliper setups. The 2002-2006 Liberties have a setup on 13 inch rotors and calipers. It would be a 17 inch rim. This way, the spacers needed for the calipers might remains at 1/4 inch, instead of the 3/4 for the Mustang.
I am also wondering how big of a boat? Also, lift? Gearing? Tires? If lifted what springs? I'd also look at steering upgrades.