1. dpkg-reconfigure -plow debconf
2. Debian uses runlevel 2
# /etc/inittab: init(8) configuration.
# $Id: inittab,v 1.91 2002/01/25 13:35:21 miquels Exp $
# The default runlevel.
...even if you are booting into gdm/kdm/xdm/entrance for a graphical login manager you can easily just `apt-get remove gdm` [or whichever one you use] and that will give you the CLI login screen. FWIW, the init script for those login managers is in /etc/init.d/
So, in Debian it is not like Redhat where you edit the inittab runlevel, you simply remove the software package that provides said login screen.
3. In order to completely purge all configuration files one option is to do
dpkg --purge name-of-package