List of question that arise for a beginner of VASP code user

1. Is it possible to mention all the four files (POSCAR, INCAR, KPOINTS, and POTCAR) in the same file?
2. How to decide single point energy calculation or geometry optimization?
3. How to decide spin-polarization and unpolarized calculations?
4. There are many Pseudopotentials given. Which one I should use for a particular calculation?
5. There are many Pseudopoentials for single atom (for example, Oxygen). Which one should I use?
6. What are the main differences between VASP 4.*, 5.2.* and 5.4.* versions of the code?
7. Where to see to know "for which atom/molecule/crystal this POTCAR file belogs"?