Issues with Layers in Storyline 3

I ran into a snag on one particular slide of the course I am currently creating.

On slide 1.3 (screenshot below) the scenario is that I have 5 buttons (each with their own matching layer).  User must visit each layer before being allowed to continue to the next slide.  I have all the triggers and variables I could think of to set but I still have 2 problems:

 §  The audio on the base layer starts playing automatically.  If the user clicks one of the buttons before the audio on the base layer ends, it plays both audio tracks at once.  (I tried setting a trigger to have the base layer pause/stop but then it wouldn’t play any audio).

§  If at any time on the base layer the user clicks the button for the last layer, it will visit the layer but get permanently stuck on the last layer.  I would like the triggers and variables set up so that once all 5 layers are visited, Storyline automatically plays the next slide. (When I tried using variables and triggers, it would skip the last layer completely and just go to the next slide).