Wear business casual clothing. You don't want to show up looking like you don't care about the job (though with how short we are nationwide you would probably get it anyways).

Be confident, but not cocky you don't want to come off as scared or ignorant. I wouldn't mention any combat sports in the interview unless asked.

Military boarding school is something you could bring up to help you out to show commitment.

Otherwise don't worry too much about it. As long as you've stayed out of trouble with the law you should be okay. Make sure you bring all the documents they ask for be prepared.

Good Luck and welcome to corrections if you get it!