Mostly so I can keep track of it, and so others know what's going on. xD
1. He has OCD tendencies. He cleans, often times cleaning up after his brothers without protest. This was likely encouraged by Splinter at a younger age, with their father rewarding him for the behavior. He also likes to keep himself very clean, however he can stand to have blood and dirt on him, especially during battle.
2. Contrary to the cartoon, he does have a tail. It wasn't there in the cartoon because it would have been too suggestive.
3. Leo's an extremely light sleeper. Any little noise can wake him up. He also has issues going to sleep, and often only gets a few hours of sleep a night, unless he's exhausted.
4 During high-stress times, he can be an insomniac as his mind is too busy to let him sleep. He will also push himself as long as he can during these times, till he just passes out.
5. He didn't get to be leader because of 'being the oldest'. He got it because Splinter saw traits in him at an early age. He's worked his shell off to get and keep the position.
6. Due to his families lifestyle, the way they've been treated, plus at least two betrayals in his life, most recent and freshest being Karai's, he's human wary. He won't completely avoid them but, if he can help it, he will stay away from them. Only exceptions are humans close to him and his family.
7. He can hold his breath underwater for at least half an hour.