Yes, Micro SD card, but only if you want loads of space for music files etc. You don't need it just for navigation. That said, I read somewhere that you can store additional routes on the card, but I haven't yet tried to use that facility, if it exists.
It will only play music in MP3 file format, too, so you may need to buy additional software to convert standard WMA files to MP3, and probably remove DRM restrictions if you bought tracks online. If you rip CDs, just save in MP3 format if your software allows it.
I can't remember the Autocom cable number, but it's a 3.5mm jack needed - older/other Garmins were 2.5mm.
Hope this helps
Yoy