hire of a harp
The harp was considered a particularly graceful and feminine instrument, permitting elible young women to show off their charms and attract potential suitors. Many upper-class women, especially those in boarding schools, learned how to play instruments like the harp to make themselves more appealing in the marriage market.
He had been an elderly man when she married him, her own age about thirty.
This was an odd match for the time. In Regency England, the average age of marriage was between 23 and 27 for women and between 25 and 29 for men.
buried two husbands
This is the first remarried woman in Austen's writing. While it was discussed in Persuasion, it was in much more generic terms, and mostly regarding men. This is an interesting dynamic.
Mr. Arthur Parker
Mr. Arthur Parker seems interested in the Miss Beauforts as earlier he thought a short walk to Trafalgar to be a lot of exercise, but he is willing to do a bit more to see the ladies. He is one of several single men in Sanditon and he is likely a contender to be a part of a marriage plot. This is assuming that, like all of Austen's other novels, Sanditon contains a marriage plot.
unfavourably
The question is why Charlotte should view the meeting between Sir Edward and Miss Clara Brereton as bad for the latter. Is it because Charlotte already formed an unfavourable opinion of Sir Edward as being a lover of Miss Clara's while talking "nonsense" to Charlotte in order to annoy Clara and appear an admirer of hers too? Charlotte finds Sir Edward tiring and may think he is, despite his title, beneath Clara. However, Charlotte does note that Clara's poverty makes her acceptance of Sir Edward's attentions more understandable. If so, then Austen is acknowledging the need for women to consider economic benefits to marriage, while also possibly giving her support to the idea of love in marriage.
poor cousin living with her
I predict that this character will be relevant to the marriage plot. The idea of a young person in this kind of circumstance reminds us of the Crawfords or Catherine Moreland. Single individuals living with relatives have, in other Austen novels, been very relevant in the marriage plots.
Links to common words/themes throughout the annotations