The offset is a poor measurement of clearance inboard, the stock specs are for a 7" wheel, which is unlike almost all wheels people go to for wider tires. I've been sneaking up on the best fit for wheel and tire sizes, I'm not close enough to know what the magic offset is with 9" wheels. but I think the offset needs to be near 20mm to get the tire close to the sway bar etc, in a 275mm tire.
You can usually use a 1/4" spacer with most wheels, but a 1/2" spacer will never fit well IMO, I think that's too much to add to the space where the forces are trying to tear the wheel off. I have 1/4" spacers, and I think those are as safe as possible for an addition like that.
I used special longer studs on my Mountaineer to fit the aftermarket off brand wheels. The hub of the wheels was too thick, so it didn't have enough threads with the spacer. You do not want to deal with longer studs, don't do it. On those front hubs, it is very difficult to remove and install the longer studs. I had a trusted machine shop do mine, because the studs were way too long and I wanted them to cut and re-thread them. The hubs are made so it is very difficult to install them straight. When I got them back, the spacers would not go over the studs, because some of the studs were not quite straight. I had to take them back and leave the spacers with them, they were fine then. But the hubs also were brand new from Ford, and the bearings felt a little loose before I ever installed them. I suspect the lifespan of the hubs will be shorter, due to the trouble they had R&Ring the studs. FYI, the only studs I found were ARP and did not have the proper OEM shank size. The Explorers have a larger stud shank/shoulder, than the 1/2" stud threads. So I had a pair of rotors cut with that smaller hole for the studs. Nobody else will go to that much trouble.
So forget longer studs, just be sure the wheels you use are very high quality and don't have extra thick hub center thickness.