If you buy Komplete, you can add libraries to it later (both NI and third party). If you buy Komplete Ultimate, you will get the ENTIRE line of NI libraries for Kontakt AND Reaktor. Of course, the third party stuff is all separate, which is probably where the HIGHEST quality libraries are.
I notice you have HALion Sonic. The Kontakt libraries are similar to Dark Planet, Hyptonic Dance, Triebwerk, etc., in that they are “expansions” to the basic instrument that can be added at any time.