The "resaleh" or "toziholmassael" is a book of fatwa (rules) that each Shia grand ayatollah must publish for his followers to describe the rules in Islam. these books are not original; most of them copy fatwas from top shia scholars of 18th and 19th centuries, most prominently among them was Sheikh
Mohammad hassan Najafi who wrote the famous fatwa book "Javaher" in 19th century address all possible rules and cases a muslim may face. Most fatwa books today are copies of Javaher, with small modifications here or there depending on the opinion of the grand ayatollah on a specific issue.
Don't be surprised about the content of Khomeini's resaleh, because you will find the same stuff in most other resalehs as they are mainly from the same sources. Khomeini's resaleh is actually called "Sharh-e tozih-ol-massael" or ("explaining the book of fatwa"), in which he explains the "Tozih-ol-massael" written by ayatollah hassan esfehani (if I am not mistaken), a prominent scholar of late 19th century.
In most cases, Resaleh is not even written by the ayatollah himself, but his students collect fatwas from different sources and show the collection to the Ayatollah for final approval. He changes what he does not accept and put his seal of approval on the rest. That's why at the beginning of each Resaleh you see the Ayatollah's signature and seal to confirm that "The content of this Resaelh was approved by grand ayatollah X".