That seems like way too much backspacing. I'd say go with 3.25 to 4 inches of backspacing to get the good mix of stance and not sticking out too far. It's too bad you have the 18 inch tires as an 18 inch wheel is gonna take up a lot of the height you could have used for tire sidewall. I personally wouldn't run a wheel bigger than a 16 on a YJ, and I'm sticking with 15s myself.
Denis A. Baldwin
1991 YJ 99 Vortec 5.7L, SM465, NP205, 14 Bolt Rear, Dana 60 Front, 5.13 Gears, Detroit Lockers, 395/85R20 46" Michelin XML tires on 20" XD Wheels, Cherokee Offset Springs (10" front to back stretch total), Bilstein 5150s, 1in. BL, custom cage, Warn M8000, Double D Dash/OHC, 4Low Front Stinger Bumper, DirtWorx Rear Bumper WTC, Tube Fenders, Comp Cut, 1 Ton HD Kingpin High Steering and PAID FOR.