If the intention was having fun, I'd let it slide. If someone damages my car on purpose, there's no need to get the police involved. I'd handle that one myself.
If you really want to plead down, hire a lawyer. It's cheaper than your insurance hike will be when the prosecutor tells you to get bent. I would not recommend going in to court without one.
Both. He should be able to hide, and you should keep the water in there. Also, you need to put a timer on the light so he's able to sleep. You should also get a bigger aquarium, because he will grow, and fast.
Have some girl hang out in your room all the time.
Or, buy a squirt gun, and train him like you would a cat. http://www.darkformula.net/files/Smilies/emot-haw.gif