I'm really enjoying this discussion of Henry's behavior and what it indicates of his character. Upon re-reading Chapter 3, I realized that I hadn't noticed this bit before:

He talked with fluency and spirit -- and there was an archness and pleasantry in his manner which interested, though it was hardly understood by her.

The rest of the scene illustrates this sentence. Mr. Tilney interests Catherine and she has a strong inclination for continuing the acquaintance, but she and we don't understand him much (any?) better by the end of the assembly.

During their conversation, I love that Catherine gets a little dig back at Mr. Tilney when he is conjecturing what Catherine may write about him in her journal and Catherine challenges,

'But, perhaps, I keep no journal.'

Brava, Catherine!

No one has yet mentioned that the most concrete information we get about Mr. T comes at the very end of the chapter when archness, pleasantry and meditations give way to prosaic practicality:

How proper Mr. Tilney might be as a dreamer or a lover had not yet perhaps entered Mr. Allen’s head, but that he was not objectionable as a common acquaintance for his young charge he was on inquiry satisfied; for he had early in the evening taken pains to know who her partner was, and had been assured of Mr. Tilney’s being a clergyman, and of a very respectable family in Gloucestershire.