The basic file layout of the "Genesis + Poser" DSON Importer and Genesis Essentials installation seems to be fairly straight forward... to me at least?

The DSON Importer program and python scripts, which plug it in to Poser, I guess, should be installed into your Poser Program Files location (the default). I'm not sure it'll work otherwise. I imagine the advanced option (to customize the install path) there is in case the user has installed their Poser Program files somewhere more exotic?

The two Genesis Essentials packages should be installed into a runtime, it would seem.

The default will be your main runtime. Go with that, you'll get a "Daz People" folder etc. appearing in the "Characters" section of your Poser Library... and a few other folders of runtime stuff. Extra dependencies are added though, far as I recall now, within the folder enclosing the runtime folder.

I just created a new runtime (or a new runtime enclosing folder, rather), and installed them into that, then added that new runtime via the usual method in the Poser Library. I'll just now keep that separate, isolated, runtime for Genesis content.

I have to say that I found the documentation that was linked to from the installer (as far as I recall) pretty reasonable...

http://docs.daz3d.com/doku.php/public/software/dson_importer/start

It didn't take me long after installing... after curiously opening up the CR2s in textedit, then the referenced python scripts, which call the DSON Loader... to get a rough handle on the way in which it was all hanging together. I do develop software for a living, fair enough. But most folk don't really need to get into all that side of it. I just find it interesting...