Spawn Different Obstacles for certain platforms

I am trying to create a game sort of like subway surfers and I want to Instantiate an obstacle every time a platform is Instantiated. There are going to be different types of platforms and different types of obstacles are going to spawn for each different platform. So, I created a gameobject array for Platforms and a gameobject array for the Obstacles. I don't know how I should go about this situation. I don't want to spawn an obstacle by using the start method from a script attached to each obstacle because I would need to use FindGameObjectsWithTag to get an obstacle array so I can instantiate an object because I'm pretty sure that FindGameObjectsWithTag uses quite a bit of cpu usage. Can you think of a way to insantiate an obstacle without using the start method?

 [SerializeField] private GameObject[] platforms;
 [SerializeField] private GameObject[] obstacles;
 [SerializeField] private Transform playerTrans;

 [SerializeField] private byte spawnAmount;

 private List<GameObject> activePlatforms = new List<GameObject>();

 private float spawnZ = 0f;
 private float tileLength;
 private int safeZone = 15;

 private void Start()
 {
     platforms = GameObject.FindGameObjectsWithTag("Platform Prefab");
     obstacles = GameObject.FindGameObjectsWithTag("Obstacle");

     tileLength = platforms[0].transform.localScale.z;
     Debug.Log(tileLength);

     for (int i = 0; i < spawnAmount; i++)
         _SpawnPlatform(0);

 }

 private void FixedUpdate()
 {
     if (playerTrans.position.z - safeZone > (spawnZ - spawnAmount * tileLength))
     {
         _SpawnPlatform(Random.Range(0, platforms.Length + 2));
         DestroyPlatform();
     }
 }

 private void _SpawnPlatform(int spawnIndex)
 {
     GameObject go = Instantiate(platforms[spawnIndex]) as GameObject;
     go.transform.position = Vector3.forward * spawnZ;
     go.transform.parent = transform;
     go.transform.rotation = Quaternion.Euler(Vector3.zero);
     
     spawnZ += tileLength;
     activePlatforms.Add(go);
 }

 private void DestroyPlatform()
 {
     Destroy(activePlatforms[0]);
     activePlatforms.RemoveAt(0);
 }

}