Skopje just might be safe enough to sleep in the streets (though we don't recommend it). There will be increased police presence for the UEFA Super Cup as well, so you have nothing to worry about. Also, most locals speak English and will come to your aid if you find yourself needing assistance.
Getting to Skopje from the airport is easy. The cheapest option is a bus that costs 3 euros. Cabs are always available right outside the airport and will take you to Skopje for 20 euros or less. You can also rent a car on spot but keep in mind that we drive on the right side of the road. ;)
Regardless of where you stay in Skopje, you will never be more than 8 km away from the Philip II Arena. Traffic is expected to be terrible on match day, however, cabs are relatively cheap and charge less than half an euro per kilometer. Your best bet will be to get to the city square early, relax, have a beer and walk the rest of the way.