Indeed, the FDC lies inside the station, (an MB8866?, can't remember), this is only some kind of interface to it, as you mention it'll be very close to the one found inside the external interface. The external one is a little more compatible as it can be used also with the FM-8.
This controller could support if I'm not wrong, four drives at a time; but I've never been able (or dare) to test it. The disk station has enough free space to be filled with half-height drives, not sure about watts of its PSU. The old 360KB drives are exactly the kind of drives you need, they are compatible with the pinout, you only need to set it to the correct disk ID (DS0 or DS1...or maybe DS2 or DS3
) and set also READY jumper (although I'm not totally sure about RDY signal being used in the FM7).