What I consider essential are: The Lyman manual, the manual from whatever bullet manufacturers you plan to use and the manual from whatever powder makers you will be using. That to me is the minimum required.
The Lee manual and those caliber (actually cartridge) specific manuals are really nothing but compilations from powder maker's free manuals and to a limited extent perhaps from bullet maker manuals. They seem to have a ton of misprints and typo errors in them generally.