Regarding the spare:
A 255/85-16 MT tire will not fit with the factory hitch, airing down and putting
a ratchet strap around it won't get it fit either. You might be able to get it to fit with a factory bumper but no hitch, I haven't tried. I have a Savage bumper that is identical from a spare tire fit standpoint, so I currently have a 215/85-16 spare (~31"), but will be fitting a 235/85-16 (~32") very soon. If you need to run an unequal size spare for very long on pavement(a few hundred miles), put it on the front axle and shift to rear wheel drive.
Regarding tire pressure:
I've been running 32psi for years with these tires, BUT, I have a full set of steel skid plates, rock sliders, and I'm always loaded up for 1-2 weeks of camping, including ~10 gallons of water. If it was a DD running unloaded, I'd probably be at 30 or even 28 psi
Maxis Bighorn MT 255/85-16, OEM 3rd gen alloy wheels. If you really, really wanted to optimize the tires to match the Limited flares, then use 1.25" spacers in front, and 1" spacers in the rear. I have 1.25" spacers all around.