1 - Just set the preview panel objects from the instance variables on the Highlight objects.
2 - The wrong answer is exactly the same as the right answer just with a not equals. You will also want to only allow it to trigger once while true.
3 - DON'T DELETE, just move them off the screen. If you take a look at my example, the highlights start off the screen and there is an on screen check.
4 - The animal text event is exactly the same as the animal event. I am not sure what your question is. If you can do the one, you can do the other.
5 - In the on-click event, just add a condition comparing the opacity = 100.
6 - Just increment the values in the events where you play the sounds. Also, if these variables are specific to the level, (meaning the count of tries is reset on each level) I would suggest not using global variables. Instead, add an instance variable to one of the objects on the layout. I would put it on the text object that displays the value. I make this suggestion because global variables are remembered between layouts so you will have to clear them on start of each layout.
I hope this gets you what you need and good luck with your project.