Lightest weight ubuntu desktop for text editing in big terminal windows?

Edubuntu is just Ubuntu really, and Kubuntu runs the KDE environment, all of those are not lightweight.

If you are going for a desktop then you might be more interested in something like lubuntu or Xubuntu. Out of those I would think that Xubuntu is the lightest, although I'm not totally sure on that. Either way, both of those are extremely light-weight and designed for older hardware

For your needs I suggest you to have Lubuntu which needs a 256MB of RAM to work as i know. If you would like to have total Lubuntu stuff then you can use

sudo apt-get install lubuntu-destop

If you don't want any Lubuntu stuff then , type this in your terminal

sudo apt-get install lxde

If you're looking for really light weight, then just skip a desktop environment altogether. You can just install Xorg and a terminal emulator such as terminator or even xterm. You don't need a display manager or even a window manager for your purposes. You can launch the emulator from X's startup script. Then, login and run startx.

If gou want a bit more look into one of the very many lightweight window managers. I used to use IceWm a long time ago, but there are lots of options to choose from.