I would never consider putting a thin wheel spacer like 5mm between the hub and wheel, it's like a washer that can work it's way loose. I believe you are overthinking it especially when you're hoping for 200K+ miles on a vehicle. At that mileage you will have already replaced most of the suspension, brakes, hub, probably axles even if you keep the stock wheel configuration. Lots of people are running 17x9 wheels with 0 or -6 or -12 offset with 37 x12.5 and 35x12.5 tires. The centering rings to reduce a 106mm wheel to the Bronco 93 is a good idea but they are usually plastic or hard rubber to be flexible enough for the minor differences like you mentioned and aren't really needed. You just hand tighten each lug to keep them centered before final torqueing and you shouldn't have any vibration issues if the wheels/tires are balanced properly. The wider track of a 0 or slightly negative offset will improve your on road handling as well. Here's a couple pictures showing trucks with several combinations:
