switching window managers and session managers - update-alternatives ?

[Jerry_Bash]

I have a question about switching between kde and other window managers (blackbox, fluxbox, ion, etc).
I am interested in learning what is the preferred or intended method of switching between kde and other 'more traditional' window managers in Debian.

I realize that kde is termed a session manager in Debian  and the others are more 'traditional' window managers.  
In looking through the files in /etc/X11/Xsession.d, it appears to me that the window manager / session manager that is started is determined by the file 50xfree86-common_determine-startup.  If a x-session-manager exists, it is used; if not, an x-window-manager file is checked, and if it exists, it is used.  If neither of these exists, a terminal is started.

I have found that I can select among different window managers, using update-alternatives --config x-window-manager, and among different session managers using a similar command for x-session-managers, but how do I select whether I want it to start a session, or use a window manager?

I am using xdm on the system currently, and it doesn't give the user an option as I believe is the case with some other login screens.  I am also interested in eliminating the graphical login as well, and logging in initially to a console and starting x from there.  I would appreciate advice on the intended way of switching window managers / session managers with that configuration (ie, using startx) as well.

Thanks in advance,
Jerryþ