You can sterilize the fruit by soaking it in water that has a campden tablet dissolved in it for about an hour. Some people use high-proof alcohol like everclear to sterilize the fruit. You can always boil and cool it, too, if you don't mind it being syrup. Be ready for the fermentation to rock and roll again once you add the fruit, no matter how you sterilize it.
As for the bucket, depending on what fruit you use, you'll probably stain it. That doesn't mean anything, though, except you've got a different colored bucket from now on. I did a raspberry wheat with 5lbs of raspberries once, and my bucket turned pink, and smelled fruity. It didn't affect the next batch I made in it, though, so I think you'll be fine.