So on ARIX, what filesystems can you use?
FFS, SFS, NTFS , FAT Currently
Does it have a terminal, a CLI or both?
Cli
Is the whole of the Unix directory structure there (/usr, /home, /etc, /var and the rest plus the Amiga directory structure?
The only place that has the Unix directory structure is the initial Ramdisk. From the user perspective only the Amiga directory structure is available.
Is Xwindows available to run unix apps? Is an emulator to run Android apps available?
No and No.