Oklahoma is fine. The reason the killing there made the news is such things are so rare there. In big cities, like Chicago, Detroit, Washington D.C., etc. the police would barely have bothered to investigate since killings are much more common. Still, the cities are much safer than when I was young in the Washington D.C. area. As long as you aren't near a ghetto area, everything is quite safe.
With an Australian accent, the girls will fall all over you.
You do need to keep your head about you, though. Alcohol, drugs, sex, and just muddle-headed thinking from students and professors can lead you astray.
If you focus on school, tennis, and healthy relationships, it can be a great growing experience.
By the way, the people in the South are the friendliest people in the country.