I can't help you with the wheel suggestions, because we were able to use stock 10-bolt semi-truck wheels on our ambulance.
But, I can tell you that we have been quite pleased with our 22.5 inch tires. So if you end up with a 22.5 inch rim, 9-10 inches wide, take a look at the DynaCargo tires. We got the Y601 on/off road tires, from Simple Tire (online). They are speed rated for highway cruising use, but also have a moderately decent tread for trail use. And their weight rating works for our medium duty truck, which formerly had 19.5 inch dual rear wheels.
Ross