@Lilybiri, I will definitely investigate the Enable/Disable method. My fear was that as I could see no "Retain enabled-ness" type option, returning to the home page would reset the button to No Action.
I have to admit I could find no guidance anywhere in the official help on using the Enable action, so aren't sure exactly what it does.
I have examples on my blog site.
Here is a possible work flow, hope I understood the result you want.
You have sequence imposed. That means you'll need to create only one variable to track. I will label that var v_counter. Give it a default value of 0, it will be incremented On Enter for the menu slide. I am not sure which version you use, so screenshots will not be possible because the Advanced Actions dialog box changed in CP2017. Create a user variable for each button: v_one, v_two...... which will be Boolean. Default value = 0. This will be toggled to 1 when a button is clicked.
Create the states for the buttons on the menu slide. When the buttion is disabled, the Rollover and Down InBuilt states will not appear, neither will the hand cursor. Be sure to check the option 'Retain State'. Personally I would keep the Normal state as 'Unavailable state', will make it easier. If the button is disabled, that 'Normal' state will be the one that appears.
Create a conditional advanced action with as many decisions as you have buttons + 1 decision, the first, that will always be executed. It assigns the value 1 to the associated user variable (like v_one) and calculates v_counter by summng all the other user variables. If only the first button has been clicked, any number of times, the counter will always remain = 1.
The other decisions are conditional, checking the variable and based on its value will enable buttons, and change state for newly enabled button to 'Play'. The buttons themselves will only have the Jump command. The Return button at the end of each part can change the state of the just used button to 'Replay'.
Hope this makes sense.