Most of the first act of the film is driven by Hugo's concern over his notebook, without which he can't complete the automaton, but we later see him rebuilding it just fine and the notebook goes unmentioned. What happened? Did Hugo just remember more of the instructions than he gave himself credit for?
Hugo's father drew it. It's one of the few things he has left of him, and therefore has immense sentimental value, regardless of practical value.
I had assumed working in the toy shop having access to all the clockwork pieces he could get his hands on is how he was able to complete it. As stated above, the notebook belonged to his father and being the only thing he had left of him he had probably read through that book in every free moment he had and had the book memorised.
Also worth mentioning is that, in the book, Hugo does eventually get the notebook back; it turns out Papa Georges faked burning it.
Did nobody notice that Hugo's uncle wasn't picking up his paycheques?
In the book it says Hugo has been picking them up and they're sitting in a pile on a desk in the room where Hugo sleeps.
Between the first and second time Hugo gets caught by the station inspector, he is walking with Chloe Moretz and takes her hat to disguise himself. How could the station inspector be soooo easily fooled by Hugo putting on a hat?
The second time he catches Hugo, he doesn't remember him as the same child from the initial escape, so it's not surprising he didn't recognise him in the middle. It's suggested pretty strongly that the stationmaster makes a habit of catching young children, so he probably just doesn't make particular note of their faces any more. As the head of security at a central train station, he probably sees lots and lots of people.
Traumatic brain injury?
For that matter, how is what's basically a Mall Cop allowed a doberman and a freakin' bullwhip?
He's the chief of security at a government-run train station. That's a bit above mall cop.
Trains stations are like airports. Security is important.
Melies built the automaton before moving into film, then dismantled it to make his first camera and never repaired it. How, then, does the automaton draw a scene from one of his films that was made after the automaton was dismantled?
Perhaps he based the scene from the film on the drawing?
I saw it as a bit of artistic license and magic. Because parts of the automaton were used to make the camera, the automaton "remembers" the major scenes and can sketch them.
Common cause. It's mentioned that Georges was the first filmmaker to use the medium to recreate dreams. He may have had a dream in his early life about a spacecraft striking the man in the moon (probably after reading From the Earth to the Moon) and it stuck with him. He created an automaton capable of drawing that dream along with his signature. When he had the technical ability later, he recreated it as a film.
At the end of the movie, Hugo is adopted by Papa Georges, so who would take care of the station's clocks now, since Hugo no longer does them?
I think we can safely assume the station just hired someone else.
What caused the fireball that killed Monsieur Cabret?