What commands can be issued to Excel for Mac from the terminal? I know I can tell Excel to open a file with: 

open MAC\ Addresses.xlsx -a "Microsoft Excel.app/"

But I cannot figure out how to do anything with Excel from the terminal.

Where can I find a list of the commands that can be sent to Excel from the terminal?
Excel is primarily a GUI application, there isn't much more you can do from the Terminal than using open to have it opening a file.

Excel has a little AppleScript interface you can use via osascript, but it only supports a minimal set of commands.