I can login to a lab Linux CLI, but have no further info on the install. Is there a generic command for starting a default DE/WM; I seem to recall "startx" would run a default X11 setup, but am looking to access a modern gui environment (if installed). Also, is there a default file explorer common to all distros?
startx is still the standard way to run a desktop environment - graphical distros set up a desktop environment to be run when X is started. If it's not set up, you may want to look into creating your own
File managers are not distro specific; very few (if any) Linux programs are distro specific, since there's nothing fundamentally different between distros.
To the best of my knowledge xorg (stareted by
startx) is the only GUI, what you might be referring to is Desktop Enviroment, that will vary from one computer to another.
Also almost nothing is common to all distros.
However you can expect bash to work more or les the same on all distros( depends on configuration files).
ls will list contents of currently open directory
dir will display name of currently open
cd will move to directory mentioned after