1. Up to you. I prefer NOT to use them for a more "realistic" look.
2. Up to you. I think even the greatest most experienced photographer still has to experiment to some degree.
3. This is popular:
http://www.playmobil.com/index.html
- You can get other access from other lines like PTE, BBI Elite Force, Starwars, whatever.
- Make your own (foam core, styrofoam, wood, plastic, whatever)
4. Try blog sites like:
http://www.imageshack.us/
Hope this helps a little and Good Luck!