The current compatible rules and source books are:
- The Hobbit An Unexpected Journey Rule Book
- Kingdoms of Men Source Book (Rohan, Gondor, Numenor, Arnor and Fiefdoms)
- The Free Peoples Source Book (Durins Folk, Loth Lorien, Rivendell and Eregion, Mirkwood, Wanderers in the Wild, White Council)
- The Fallen Realms Source Book (Isengard, Harad, Easterlings, Umbar)
- Mordor Source Book (Everything Mordor)
- Moria & Angmar Source Book (Moria Goblins, Spirits of Angmar)
These are the most updated versions of the rules yet. The Hobbit rulebook has new rules and also changes a few of the old rules as well so a big recommendation to have one of these. The new source books summarise all the army lists and are needed for older profiles as the The Hobbit Rule Book only contains profiles for Hobbit miniatures. New deployment rule for SBG is that 1 Hero + 12 or less warriors = 1 Warband. Keep this in mind when creating armies but all the newer source books explain this.
As for the older books and things you have, I suggest keeping them as some stuff like painting guides and terrain making are missing in the newer books. The legions of middle earth book is out of date and shouldn't be used to create armies due to out of date profiles and deployment rules.
Hope I answered your question