Hide/Show Buttons

That is one approach. I typically do NOT hide the next button but instead cover it with a grayed-out version. When someone clicks on the grayed-out button, a msg is displayed that tells the learner what they need to do to proceed. Leaving a blank space can leave someone thinking that the button is missing or they might not be sure just what they have to do to proceed.

Typically what I do is have an action on each button that adds a different letter to a variable. Button 1 adds a, button 2 adds a b, etc. Then there is another action that hides the grayed-out next button with multiple conditions - Variable contains a, Variable contains b, ... ALL of the conditions have to be satisfied before the learner can proceed.

I usually do several other things. I display a check mark beside each button once it has been clicked. I also have a page level On Show action that is the same as the one on the buttons that hides the grayed-out next button when all conditions have been satisfied. This way if the learner comes back to the page they do not have to click all the buttons again.