Do you have to install Aquarius to make the libraries work? forgive me could someone explain how and what is needed to install everything?

Some yes, some no. There are 2 types of libraries: Officially supported libraries (which you install via the Aquiarius app) and 3rd party libraries (which you download from their website and install manually).

If you open the Aquarius app then it will break this crack i'd imagine. So that means officially supported libraries are out the window for using on this release.

3rd party libraries should be fine to use because the installation for those is about as primitive as it gets - just manually put the files in the right folders yourself.

And that's what is meant in the title of this release when it says (External Libraries Only). They mean that only 3rd party libraries will work. They just phrased it weird

In all honestly the 3rd party libraries are the heart of N4 anyway, they're just as good if not better than the officially supported ones. In fact, 3rd party libraries are the reason i bought N4. I don't own any officially supported Acustica libraries even though i could if i wanted to. I bought 3rd party libraries exclusively

Support the 3rd party devs where possible

Nebula3 era third party libraries (called presets) will work in Nebula 4/4.5. But, there are reports of some not working with newer macs OS's. I run macOS 10.13 and can load N3 era presets (AU) in N4/N4.5 with no problems.

https://www.magesy.blog/download/presets-patches/nebula-plugin/