While it's tempting to connect devices like external HDDs, keyboards, or mice to your Mac mini’s FW800 port using adapters, it won’t work as expected. FireWire (1394) and USB use different protocols, and simple adapter cables can’t translate these signals.
The chain of adapters you mentioned just changes the connector types, but it doesn’t convert the protocols. Even if you connect everything, your Mac won’t recognize USB devices through FireWire.
To safely use USB devices, it’s better to stick to the Mac mini's USB ports or look for a proper ***FireWire-to-USB protocol converter*** (which is rare).