I have DS3A, so I don't know how things work in DS4.  If you purchase something the download comes in an installer.  I have set up runtimes outside of the program to keep things catagorized: Character, Clothes, Props, ect.  I install the content into each folder with the installer using the customized installation option.  To find my content in DS3A, I have it set up that the program finds all content upon opening- to do so you can either set it up that way upon installation of the application or go into the runtime folder options (the arrow at the left side of your content library) and do a search depending on which directory it's in.

My content is on the external HD rather than the C drive. It keeps my computer's memory open for rendering.  I can find the runtime folders because I have Studio set up to make sure and find the F drive when it starts.

When you save the scene for the character, that's the scene file yes.  To save a character setting (morph) you can use the PFE (Poser Format Exporter) which is free from Daz3D.com to make the actual injection files and place them where you want them in your runtime.  Just remember to make the file name simple.  Example: M4 Head Inj.pz2 or M4 Complete Inj.pz2.  You can make a png image in photoshop or gimp so you have an icon in your runtime-save it with the exact same name you've given the inj file however or it won't work.

(I generally just keep my characters in the scene file saves- I don't need to make injection files unless I'm giving away a morph set or have a character set I want to sell.)

To save a pose rather than a scene you can use the PFE exporter as well.  Rather than make a pz2 injection file, you'd use the .cr2 I believe.  I haven't bothered to try to save a pose outside of the save to the scene file, if someone else knows this for sure please chime in.

I prefer to save my characters using the scene file, on their own, with no hair or clothing or props in the scene.  That way if you plan on using him/her again you just find the scene, open it up, and start from there.  Easy-peasy.  I also have a separate scene file for M4, M4 Enhanced and V4, with all the morph sets for each character already injected into them.  No clothes, no textures, nothing but the injections; to save time and keep my workflow smooth it just seemed logical to me.

If you have any questions I can help with, feel free to ask!  Either here in the forum or message me.  I don't bite.

Often. ;)