The first problem looks resolved as it spawns one only based on the logic. To use a range you can use random(x,y) where x and y would be the left and right co-ords of the box.
For the second problem you need a parameter sent through the function, they are useful things. When you call a function it doesn't pick instances from the previous actions, to get around this you send the enemy UID through the function as a parameter. Then inside the function event you add a condition to pick enemy where enemy UID = parameter, this will pick the one you clicked on originally.
For the third problem at its simplest you could use choose(1,2,3,4) which would set an answer from a choice of answers or you can look at Arrays where you can store many answers kind of like a spreadsheet and pick from them.