To answer some questions. Yes v4 is a base figure. If you already had this figure in your DAZ library you can simply add this library to poser. At the top right of the poser library there is an icon that looks like books with a plus sign, click on this and a window opens, (not sure what it's called on a Mac). Navigate to your DAZ library, click ok and this library will be added to your list of poser libraries (at the start you will only have poser 11 content library and downloads library)

v4 is one of the more awkward things to install in poser as it has to run a batch file if you want to set it up to use various morph packs, the DAZ dim does this for you though. You can set the DIM to install where you want)

In general for stuff from DAZ you have to manually unzip it and then merge the runtime folder with one of your runtimes which is set up as a library in poser see this tutorial as to how to add libraries in poser (This is for native poser content, not DAZ content that requires DSON plugin)

https://www.youtube.com/watch?v=y3y6ElYNshk&list=PLHskz2PNix3Alw_gLu1_ezbQGg7kqUFVZ&index=1

Yes poser has lots of other base figures, some come with poser while other have to be purchased separately. You can then apply character packs to these to change their appearance, but character packs are for specific base figures, so a v4 character pack won't work on LaFemme etc

To install content purchased here at rendo and most other stores poser has a function in the file menu, install from zip archive. Some free stuff will work correctly with this some won't, to work correctly the runtime folder must be one of the top level folders in the zip.

File not found is poser saying just that, you can often find the file manually.

ok when you render and then want to save the render, you should be able to do this, in windows you right click on the thumnails and it give you the option to export and when you do it give you the option of choosing a file format.

A cr2 file is a poser file that defines a character , so it will specify the geometry and texture files amongst other things.

An obj file is a geometry file which defines the figure mesh

All this is rather brief but hope it helps