Question: What did Jezelle mean at the police station about the creeper saying "I think it's eaten too many hearts for its own to ever stop."
Question: Where would the monster get the fuel for his vehicle? Surely he wouldn't be fueling up at the gas stations.
Answer: There's no reason he couldn't use a gas station. In the dark he just looks like a guy with dark skin, unkempt hair, and a trench coat. Even if somebody does get close enough to get a good look at him, he would easily kill them to keep his secret.
Question: How did the creature get the vanity plates "BEATNGU?" Sure it's creepy, but can you imagine that thing standing in line at the DMV?
Answer: You can purchase vanity plates by mail, or it stole the truck.
Answer: The Creeper possibly has some skill in metalworks. Perhaps it created this custom plate as a mocking or darkly humorous touch to his truck. This is the explanation offered in the Creeper's bio page on Villains Wiki.
Answer: Considering that the entire story is pure supernatural fantasy, anything is possible.
Answer: Since the Creeper needs various body parts i.e. eyes to see, lungs to breathe, it would also need to eat the hearts of its victims for its own heart to keep beating. Or she could mean that the Creeper is essentially devoid of all emotions as it keeps attacking anybody that has the body parts that it needs to extend its own life.