1. spawn current wave:
- store current wave number in one variable and have function that will check which wave is active and spawn enemies accordingly
2. check if current wave is killed:
- you can do it by putting all enemies into one big family and check how many instances of enemy are available, when that number is zero go to point 3.
3. add 1 to your wave variable and then go to 1.
Very general answer for very general question