If you are using the SD-Card Linux Image provided in this site https://communities.intel.com/docs/DOC-22226, the image includes iwlwifi-135-6.ucode and iwlwifi-6000g2a-6.ucode, this means if you are using the N-135 you don’t need to install the firmware, because it is already included in the image. If you build your own image I think you need to do this manually, if you need the drivers you can get them from this site http://wireless.kernel.org/en/users/Drivers/iwlwifi, then just put them in /lib/firmware. In order to test if you are booting up from the SD card you can upload the Blink sketch as you mentioned. Then when you reboot your board as soon as the board finish booting up it should resume the blinking. I hope to have covered all you questions.