all of them
if it is not bugged up too much
Mods (modifications) are free. You do not need to pay, however, you do need to be able to download them. Use Magic Launcher or Forge to do this.
All mods are compatible
The Yogbox is not compatible with any mods as of now.
Go on minecraftforum.com and download it from there.
darude - sandstorm
nothing
Yes, you can install as many mods as you want as long as they are compatible with each other. Some mods use the same .class files which basically means they aren't compatible. You will know if two mods are compatible with each other because your game will give you a black screen and you won't be able to play until the mods are deleted.
no
no
Check the forums for your other mods to see what mods they are compatible with.
no
versions -> 1.6.1 -> 1.6.1 -> 1.6.1.jar -> there you put your files