He is very handsome! Bri, you need to know he some day may not get along with Lily. You need to be prepared to seperate them permanently. It's a HUGE commitment. He may never learn that cats are off limits either. Please get a breakstick ASAP. It's better for you to have one, than him going after Lily or your cats and you cannot get them apart and he can do more damage to your cats and Lily than they can since they are little compared to him.

The breaksticks are only to be used with pit bulls though, not other breeds. No dog parks or dog daycares for him either! I really hope it works out, but you need to sit down with your mom and really think about it before making such a huge commitment and have her look at these links as well so you are on the same page. I know you said he is your responsibilty, but she may learn some things too about this wonderful breed.

http://www.pbrc.net/breakfight.html
http://www.pbrc.net/shop/bsticks.html
http://www.pbrc.net/multidogs.html

http://www.pbrc.net/rotate.html

Doing intros the right way:
http://www.pbrc.net/training_cat_dog.html
http://www.pbrc.net/dogintros.html

http://www.pbrc.net/training.html

http://ahimsadogtraining.com/blog/leash-walking/

You also need to make sure your house insurance will cover a pit bull. Check into it, if you're keeping him, you will have to get insurance that covers him.
http://www.badrap.org/insurance-providers

http://www.badrap.org/node/97
http://www.badrap.org/what-expect