How do I require user to manually move project slides forward?

To me this is the easiest way:

• Open the Master slides, and choose the Main master slide (bigger than the other master slides)
• Add a shape button to that slide: you could make it invisible (by setting Alpha fill = 0% and stroke width = 0), or use it as a Next button.
• Check in the Options of its Properties panel that it is pausing the slide; it will automatically pause the slide using this main master slide at its end, whatever its duration.
• If you use it as Next button, keep the command 'Go to Next Slide' which is the default choice, if you only want to use that button to pause, you can choose No Action

Work flow is also described in this article:

Pausing Captivate's Timeline - Captivate blog