*SD-Card: I think a ultra-quick SD card is not needed since the camera is using H.264 video codec (high compression means small file size or less KB/s transfer rate). What you need is a very fast computer to watch the movies (or a graphic card with a H.264 hardware decoder + a supported player, e,g, recent nVidia + VDPAU enabled mplayer on Linux)
*Battery: If you charge the camera via USB connector of a PC the battery will not be fully charged (due to the 500mA restriction of USB port). So a separate power supply is recommended. Typical the battery lasts for 50-70 minutes depending on external temperature etc.
*Anything else: GoPro states that the housing is waterproof until 60 meters. But the camera can not fix focus underwater with this case. So for underwater usage you need a separate housing with a flat lense (the standard case is useless underwater!).