HHD is only for 3ds. You don't need an SD card to play it unless you want to get a downloaded copy instead of cartridge and you don't have space on the default sd card on your ds. You don't need amiibo cards for this game, although they do have a function for the game. You can still play it without them to it's full extent.
You don't need amiibo figurines or cards to play the game. The amiibo features means you can get special characters and more control over when some villagers appear, but you can already get all the regular villagers without it.
I believe the game usually comes with an amiibo card for free and there have been promotions in shops where you get free amiibos or free extra cards, I think.