I believe RAI, Snap Kick is supposed to be limited to once per round. But you're obviously going by RAW. So, in that case, the -2 penalty will stack. 3 snap kicks in a round means -6 to all attacks. Depending on the power level of the game, as a DM, I would make one of those two rulings.
No, you cannot use as swift action and immediate action on the same turn. An immediate action uses up your next turn's swift action, so if you use an immediate during your turn, that's the turn that loses its swift action. You could use the immediate action right after your turn, using up your swift action for your next turn, however...
Where is Shadow Pounce from?