If you have only a single slam attack for all of your natural attacks, then yes, it does. If you have '2 slams' or a slam and some other natural attack, then no, it does not.
They do not. You can have as many primary attacks as you want and they will all have the same attack bonus (barring any specific Weapon Foci or other modifiers that only apply to one attack type). Secondary attacks are the only ones that take a penalty of -5.
