You can use xdg-open to open files and directories from the command line. I have an alias of
xopen to make the typing a little easier. Put this in your
~/.bashrc to do that, and to have a root file browser using sudo:
alias xopen-root="sudo xdg-open"
It will open the file in the application that would be used if you double-clicked on it. For example, if you named a text file, it would open in gedit. And if you pass it a directory, it will open the file browser. So if I am in my home directory I can do
$ xopen Documents
$ xopen .
and the file browser (nautilus for me) will open that directory. Also note that xdg-open will return immediately - the new program is launched as it's own process and you can type in your next command.
To open a terminal from the nautilus file browser, you should install the
nautilus-open-terminal package. Then you can right click on a folder, or in the blank space below the files, and open a terminal with the path set to that directory. Not sure how to make it a root terminal though - I always just use sudo myself.