[robespierre]

If you haven't found it already, many of your beginner questions are in the SGI hardware FAQ from the 1990s.

The "barcode" beginning 080069 is the Ethernet MAC of the primary Ethernet, which is the System ID. It has no known correlation to the system configuration as it is just a sequential ID.
The CMN... code is a FCC ID. SGI used CMN as its vendor designator and B015 is a hardware platform number (Octane). The rest is a configuration, in this case 300 MHz for the CPU.

Software compatibility is generally good, although very early (pre-1992) programs probably won't run on IRIX 6.5, and there are some other programs that were incompatible with later graphics cards.