Mass Effect-like Dialogue: Written with Numerous GUIs or within Script?

Hello,

I'm making a topdown game that centres around dialogue trees. I developed a small prototype using numerous GUIS to express each branch. As you'd imagine, this led to a lot of GUI panels. Now that I'm working on an alpha, I'm wondering, is this the best way to go about dialogue trees?

I hear you can rewrite the text in a GUI by using script. That sounds possibly better, but what if I wasn't sure on the sizing of my buttons and such? Sounds like polishing could be hard...

How should I go about this? And if through script, how would that be written?

Also, bonus question--how would I program the arrow keys to highlight a dialogue choice so 'Z' would activate it (if there are always two choices beside each other and holding the 'left arrow' would highlight the first choice for example)?