How do I split my game into separate levels

I've created a very simple balloon popping game like the first example in the Level Zero eBook. Basically I randomly spawn balloons that head to the top of the screen and the player gets points for tapping on them.

At the moment I am increasing the speed and rate of the balloons every X seconds. What's the best way to split this up into different levels so that each is more difficult? Duplicate the layout and event sheet for each level? Make multiple layouts with one event sheet? If there's only one event sheet how do I keep track of what the current level is? Do layouts have variables?

I would say, whichever is easier for you to keep track of...

You don't even have to have more than one layout if didn't want. You could have all the other "levels" backgrounds as sprites that are hid until needed on the one layout. You could keep track of the level by using a global variable or a "brain" object with instance variables on it. Then your one event sheet would simply change the speed based on level variable and set which level is reveiled or hid based on it as well.

That makes sense. I'll need to look into arrays but I'm guessing I could use an array to store things like level1_speed, level1_rate, level2_speed, level2_rate, e.t.c. instead of having separate variables for each.

It would be easier if your speed was relative to the level... then all you would need to do was store level value in a varaiable and then use a formula to set the current level's speed.

Ie. Speed=Level+50x100/Power-random(1,100)