To be compatible for the future, you should update the firmware of the Fireface 802 to make it compatible with the new DriverKit USB drivers. Apple will stop supporting the kernel extensions, which includes the Firewire driver, in the future.

No thunderbolt adapter! Simply an USB-B to USB-C cable or a common 'old style' USB-B to A cable with an adapter to USB-C.
The combined ports on the Mac accept USB connections as well as thunderbolt. Both technologies share the same plugs and ports but are different furthermore. So actually you also could use the FireWire port on the 802 and connect it this way to the Mac, using the assumed adapter. But I wouldn’t suggest that because for firmware updates you need the USB connection anyway. Also there are only kernel extension drivers for FireWire but not the 'new generation' driverkit ones.
Important is the already suggested firmware update (over USB) to make your interface ready for the new driver versions!