First, don't move anything! 

This will save you the heartbreak of having to reinstall everything. 

1. V3 base comes with all those figures you mentioned; V3 SAE is the actual base model, V3 blank SAE is the basic mannequin model, and Vicki 3 to Vicki 2 SAE is a model which accepts V2 skin textures.  The model to use is V3 SAE.

2. Yes, you absolutely need to purchase the head and body morph packs to change the physical appearance of V3.

3. Expressions Inj is an injectable morph pack which adds different types of facial expressions to V3.  It would make sense to place this into the Expressions folder, but because it populates V3's properties with spinning dials which controls the level and intensity of facial expression.  The poses in the Expression folder only applies just one expression per icon.

4. !MAT V3 folder only contains textures which are applied to the V3 base model.  They are referred to as second skin, they are not really actual clothing models.  They should remain where they are because they are called MAT Poses or material poses.

5. Hair is not part of the package; they are obtained either through purchase or free.

The installer does not arbitrarily dump content into Poser.  They are placed into those folders for a particular reason and many of them have absolute paths to additional content and geometries not visible in the library.  Until you become more familiar with how content is distributed within the runtime folder, I would suggest leaving them where you find them.  Since you are also starting with a very robust version of Poser (PoserPro 2010), you should pay very close attention to the information posted in this forum.  Much of it will be over your head, so be prepared to ask plenty of questions.