GUI for ubuntu server: xfce or xubuntu-desktop
Both are metapackages but xubuntu-desktop is a metapackage for much more stuff than the other one that is just for the desktop environment, xorg and few minor things. You can read about the difference between a package and a metapackage here. In short metapackage does not contain anything else than references and what matters is what metapackage refers to (metapackage claims to depend on them and asks that list to be installed).
So I guess your first option would not install anything. If you really want the minimal solution then go with xfce for which the correct command would be:
sudo apt-get install xfce4
Just add anything else one by one according to your needs. Also if you have xfce4 installed you can always expand your install with xubuntu-desktop that would just add lots of stuff.
You could also consider using Webmin or Zentyal for web based server management.
First, sudo apt-get install xfce returns:
E: Unable to locate package xfce
If you run apt-cache search xfce you'll get a longish list that includes
xfce4 - Meta-package for the Xfce Lightweight Desktop Environment
and
xfdesktop4 - xfce desktop background, icons and root menu manager
I suspect you may want either xfce4 or xfdesktop4 instead of xubuntu-desktop.
Next, you can look at the description for both xfce4 and xfdesktop4 using:
apt-cache show xfce4
and
apt-cache show xfdesktop4
I'm pasting part of the output for apt-cache show xfce4 below:
Description-en: Meta-package for the Xfce Lightweight Desktop Environment Xfce is a lightweight desktop environment for unix-like operating systems. It aims to be fast and lightweight, while still being visually appealing and easy to use. Designed for productivity, it loads and executes applications fast, while conserving system resources.
This package is a metapackage; it depends on the core packages of the Xfce4 desktop environment and recommends some extra Xfce4 packages. If you intend to use Xfce4 and want the full experience then installing this package and the packages it Recommends is a great place to start. If you just want to pick and choose the core components then feel free to remove this package.
Next, you can run the following commands:
sudo apt-get install -s xfce4
and
sudo apt-get install -s xfdesktop4
Then inspect the output and judge for yourself. Nothing will actually be installed because the -s ensures it's just a simulation.
My feeling is that you should install xfce4 and see if you're satisfied.
Both xfce4 and xubuntu-desktop are meta packages and you can find out what files any package contains, what packages are required, what packages are recommended, what packages are suggested and what if any packages it conflicts with by searching from here.
http://packages.ubuntu.com/
If you compare the pages returned for xfce4 and xubuntu-desktop you will see that xubuntu-desktop depends on most of the same packages as xfce4 and a lot more besides.
sudo apt-get install xfce4
Will install a lot less than
sudo apt-get install --no-install-recommends xubuntu-desktop