Regarding GUI Vs Text log in:
-- GUI is not standard for "Linux", it is standard for some Linux Distros and is an option in many more. You should take a look at XDM, KDM, or GDM if you want a graphical login.
Regarding X-Windows instead of KDE:
The X Window System (which is not called X-Windows in any official manor) is the lowest level of most *NIX systems. KDE is a desktop environment that you can run on top of it. I don't believe it is possible to run KDE without X.
Regarding changing the Window Manager:
On most Linux systems (and therefore I assume FreeBSD also) you can create a file called
.xinitrc in your home directory containing a list of commands to execute when the startx command is typed. There is an example file in the Linux Config section of
http://david.us-lot.org/
Regarding the desktop being larger then the resolution:
Edit your X config file (man XF86Config-4 to find out which file this is). Remove resolutions you can't use from the list, place the highest resolution you can run at the left hand edge of the list.