Your case is the correct one. Please take a look at the user manual for assembly instructions:
Because of the limited space, you can’t directly use a full-size SD card. micro to SD adapter is included in the kit. Any micro SD card of 4GB or above should work fine. If you already have a full-size SD card, you can flash the image, make sure it works, and then cut it in half:
There are also other low-profile SD card adapters available for RPi.