On the subject of the size of Longbourn and the Bennet's income, there is a book called A General View of the Agriculture of Hertfordshire, published in 1804, which has been scanned into the Internet Archive. It says:
So! There were probably fewer than ten wealthier families in the entire county. (However, estates in this county are smaller than in other parts of England, so having a large estate for Hertfordshire is not saying much compared to Darbyshire or Kent or other places.)
There is also an essay by Bethany Delleman, "Could Mr. Bennet have Saved Enough for Decent Fortunes on his Income?" which has scans of a book from 1823, A System of Practical Domestic Economy. It lays out a proposed budget for a family of five in 1823 (two parents + three children), and assumes that they will be able to live well and have a large household (ten servants, five horses, a carriage and a chaise) on 1800/year, while saving 10% (200 pounds) for emergencies and savings. Now, this is not directly comparable to the Bennets, as it comes from at least a decade after P&P, and maybe over two decades (depending on whether you think it is set when Austen wrote it in the late 1790s, or when it was published in the 1810s). Still it gives us something to go on, at least. And it's not as if the proposed 10% savings would actually go into savings every year; emergencies happen. But saving a significant chunk every year is seen as a normal thing for a family of the Bennet's wealth to do, or at least something they ought to do. And the Bennets ... haven't.
PROPERTY in Hertfordshire is much divided; the vicinity of the capital; the goodness of the air and roads and the beauty of the country, have much contributed to this circumstance, by making this county a favourite residence, and by attradling great numbers of wealthy persons to purchase land for building villas: this has multiplied estates in a manner unknown in the more distant counties. About 7000I. a-year is the largest estate in the county: there are six or seven from 3 to 4000I.; more of about 2000I.; and below that sum, of everv value.
So! There were probably fewer than ten wealthier families in the entire county. (However, estates in this county are smaller than in other parts of England, so having a large estate for Hertfordshire is not saying much compared to Darbyshire or Kent or other places.)
There is also an essay by Bethany Delleman, "Could Mr. Bennet have Saved Enough for Decent Fortunes on his Income?" which has scans of a book from 1823, A System of Practical Domestic Economy. It lays out a proposed budget for a family of five in 1823 (two parents + three children), and assumes that they will be able to live well and have a large household (ten servants, five horses, a carriage and a chaise) on 1800/year, while saving 10% (200 pounds) for emergencies and savings. Now, this is not directly comparable to the Bennets, as it comes from at least a decade after P&P, and maybe over two decades (depending on whether you think it is set when Austen wrote it in the late 1790s, or when it was published in the 1810s). Still it gives us something to go on, at least. And it's not as if the proposed 10% savings would actually go into savings every year; emergencies happen. But saving a significant chunk every year is seen as a normal thing for a family of the Bennet's wealth to do, or at least something they ought to do. And the Bennets ... haven't.