When Sharpe tells Harris to go home and write a book with lots of shooting in it and he will become a rich man. This is a direct reference to what some of the 95th Soldiers did do after the wars were over, and some did indeed become rich, due to the hero status that riflemen had at the time. One of those was Rifleman Benjamin Harris, who the character is loosely based on (though he is not actually meant to be the real Harris). An audio-book version of Benjamin Harris's 'Recollections' has been recorded by Jason Salkey, who plays his fictional alter ego in the Sharpe films.
Author Bernard Cornwell named his hero Richard Sharpe after a famous British rugby player; the character of Leroux, his nemesis, was named after a South African player who broke Sharpe's ankle during a game.
In the novel of the same name, Sharpe fights at the famous Battle of Salamanca. In the film, the setting is changed to a key fortress in a town called Villafranca. In reality, there was a town of that name in Spain that saw action during the Peninsular war, but much earlier and without British involvement.
Father Patrick Curtis was a real person, born in 1740 in Ireland. He served as rector of the Irish College in Salamanca, along with the University of Salamanca, where he was known as Don Patricio Cortés. For his services to the British Intelligence in Spain, he received a pension upon returning to Ireland, and served as Archbishop of Armagh and Primate of All Ireland from 1819 until his death in 1832.