How to make infinite enemies spawning wave system?

I really didnt want to code the entire thing but ended up getting carried away. This is the jist of it:

 private int wave = 0;
 private int numOfTotalWaves = 10;
 private int numOfEnemyTypes = 3;
 private int[,] waveSpawnCount = new int[numOfTotalWaves, numOfEnemyTypes];
 private int aliveEnemies = 0; // Will count how many enemies are currently alive, MAKE SURE TO HAVE THIS DECREASE WHEN ONE DIES
 
 void Start()
 {
     //Set Wave 0 to 0 spawns because we dont want anything to spawn in wave 0.
     waveSpawnCount[0, 0] = 0;
     waveSpawnCount[0, 1] = 0;
     waveSpawnCount[0, 2] = 0;
     
     waveSpawnCount[1, 0] = 10;    //Store that we want 10 of Enemy 0 to spawn in Wave 1
     waveSpawnCount[1, 1] = 0;
     waveSpawnCount[1, 2] = 0;
     
     /*
     ...
     And So On
     ...
     */
 }
 
 void Update()
 {
     if(aliveEnemies <= 0)
     {
         if(wave <= numOfTotalWaves)
         {
             wave++;
             SpawnWave();
         }
     }
 }
 
 private void SpawnWave()
 {
     for(int enemyType = 0; enemyType != numOfEnemyTypes; enemyType++) // For every enemy Type
     {
       for(int i = 0; i < waveSpawnCount[wave, enemyType]; i++) // and for every number of units to spawn for that enemy type
       {
           SpawnEnemy(enemyType); // spawn that enemy type
           aliveEnemies++; // Add one to our alive enemies counter
       }
     }
 }
 
 private void SpawnEnemy()
 {
     switch(enemyType)
     {
         case 0:
         // Do whatever you do to load enemy 0
         break;
         case 1:
         // Do whatever you do to load enemy 1
         break;
         case 2:
         // Do whatever you do to load enemy 2
         break;
     }
 }

As for the wait 5 seconds and spawn more stuff thing. You have two options for expanding on the code that I've provided that I can think of. Either 1. Just include these things in the regular waves, this will get messy and isnt recommended but if you're just throwing something together quickly it'll probably be a easier/quicker solution. OR 2. Have a 2nd 2D Array (the thing where its int[,] that stores the values you have for "extra" waves - basically just duplicate everything there and rename the new ones to extraWaveSpawnCount or something like that and store the numbers you want in there and do the same thing as I do with spawning the regular wave except after a delay. You can save the delay in another array as well. ie private float[] extraWaveDelay = new float[numOfTotalWaves] then extraWaveDelay[0] = 0.0; extraWaveDelay[1] = 5.0f and have the current wave delay decrease by deltaTime by doing extraWaveDelay[wave] -= Time.deltaTime in Update and then if(extraWaveDelay[wave] <= 0) ... SpawnExtraWave(); etc.

Hope this helped.