"Don’t try to think in terms of GUI and keep the functionality on console...

"Don’t try to think in terms of GUI and keep the functionality on console level only."

"The shell script will be GUI based, much like a package manager allowing user the ultimate level of interactivity."

You have contradicted yourself there.
If this is your homework, please go and try reading the bash tutorial on line :
http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-1.html or :
man bash
if you would like something to read off line.
Should you not need a gui.

If you do need a gui, take your pick : QT Ruby, phpgtk, pyqt, pygtk, pyfltk , tcl\tk or perl. All shell scripting language incarnations, libraries or tool kits which are useful for the task.
Lots to choose from but don't use bash if you require a user interface. It's not designed for that. The only useful shell user interface library is ncurses : http://www.gnu.org/software/ncurses/ but you'll maybe find learning python, ruby, perl or php more useful though.

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