I have always thought that Mr Bennet was having a joke with Lizzy, but have now decided that he may well have had a more serious intention in warning Lizzy of the pitfalls of falling in love with Mr Wickham (from a prudential point of view of course).

I also think that Mrs Gardiner cautions Lizzy not to disappoint her father because (a) he is the parent Lizzy most respects and (b) I doubt that Mrs Bennet would be able to see past the point of having a daughter married and would not consider if Lizzy and her husband would be beggars, so long as she was married!