Creating an interactive button/text adventure [on hold]

I'm looking to create something to similar to this, where you can select a button and have a dropdown of text. I've noticed a couple things to implement that I'm wondering how to do:

• Button revealing text: I think jQuery's slideDown() could be used for this.
• Progress bar on right side: This one I have no idea, some sort of color changer that updates on button click perhaps?
• Autoscroll down on button click: is this perhaps one of scrollTo() or scrollIntoView()?
• Fixed Choice: Clicking a button means you can't change your decision. This one I also have no idea, but perhaps a way to disable clicking the previous button after a selection is made?

Any advice or feedback on the approaches I'm taking for any of the four main parts would be helpful. Thanks!