I think boxing is a good way to start when thinking about how Supes should fight. There are very many different methods and types of boxers. If Faora and Zodd know martial arts and Superman ends up with a style similar to boxing he could still hold his own.
I agree. Boxing is a very American fighting style. When most kids play fight, they usually imitate boxing and some wrestling. That's basically what I think Clark would have grown up with. I don't think Superman would be that interested in martial arts because he doesn't really have a fighter mentality. More often than not it's his last resort.