State of Next Button based on count Variable

Center is right; variables hold their value from slide to slide.  You could reset the count variable to 0 at the beginning of each slide, or use new variables. 

The next problem you will run into is that the learner can advance by clicking one hotspot three times, or one once and another one twice.  This solution involves a bunch more work, but if you want it to be foolproof, it's worth it.

The principle is that rather than incrementing a variable (which is vulnerable to over-counting), you need to count only those objects that have been chosen.

See the attached sample. Using the calculation layer saves having to create a gazillion triggers. I duplicated the slide, and the duplicated slide worked without modification.

You can use the slide. All you have to do is to change the picture, and the size and location of the shapes. I used shapes instead of hotspots, because hotspots can't have states. nothing else needs to be changed.

Any questions, ask.