Delegates & Events registration & deregistration - Doubt

Hello,

Two Classes

1. ObjAEventHead.cs

2. ObjBEventListener.cs

SCENARIO :

Awake() & OnEnable() on ObjAEventHead.cs is called before Awake() & OnEnable() on ObjBEventListener.cs It is a wierd way Unity calls these methods. When I use Delegates, Events or Actions, my habit is to register a listener in OnEnable & DeRegister in OnDisable like in the below scripts.

ObjAEventHead.cs

 using System.Collections;
 using UnityEngine;
 
 public class ObjAEventHead : MonoBehaviour 
 {    
 
     internal delegate bool? KeyPressHandlerWithReturnValue();
     internal event KeyPressHandlerWithReturnValue OnKeyPress;
 
     internal static event KeyPressHandlerWithReturnValue OnKeyPressStatic;
 
     internal System.Action<bool> OnTestingAction;
 
 
 
     float time = 0f;
 
     private void Awake()
     {
         Debug.Log ("Obj A Awake");
     }
 
     private void OnEnable()
     {
         Debug.Log ("Obj A OnEnable");
     }
 
     private void OnLevelWasLoaded(int _index)
     {
         Debug.Log ("Obj A Level was loaded");
     }
 
 
     private IEnumerator Start()
     {
         while (true)
         {
             if (Input.GetKeyUp (KeyCode.A))
             {
                 if (OnKeyPress != null)
                 {
                     var goat = OnKeyPress ();
                     // Only the last trigger module's return value is printed
                     Debug.Log (goat); 
                 }
             }
 
 
             if (Input.GetKeyUp (KeyCode.S))
             {
                 if (OnKeyPressStatic != null)
                 {    OnKeyPressStatic ();}
             }
 
             if (Input.GetKeyUp (KeyCode.B))
             {
                 if(OnTestingAction != null)
                 {
                     OnTestingAction (true);
                 }
             }
             yield return null;
         }
 
         yield return null;
     }
 
     private void Listener()
     {
     }
 
 
     private void OnDisable()
     {
         Debug.Log ("Obj A OnDisable");
     }
 
     private void OnDestroy()
     {
         Debug.Log ("Obj A OnDestroy");
     }
 }

ObjBEventListener.cs

 using System.Collections;
 using UnityEngine;
 
 public class ObjBEventListener : MonoBehaviour 
 {
     public ObjAEventHead ObjA;
 
     private void Awake()
     {
         Debug.Log ("Obj B Awake");
     }
 
     private void OnEnable()
     {
         Debug.Log ("Obj B OnEnable");
         ObjA.OnKeyPress += keyPressListenerFromObjA;
         ObjA.OnTestingAction += onTestingAction;
     }
 
     private void onTestingAction (bool obj)
     {
         Debug.Log ("Action Received - " + obj);
     }
 
     private bool? keyPressListenerFromObjA ()
     {
         Debug.Log ("Obj B Listener");
         return true;
     }
 
     private void Start()
     {
         
     }
 
 
     private void OnDisable()
     {
         ObjA.OnKeyPress -= keyPressListenerFromObjA;
         ObjA.OnTestingAction -= onTestingAction;
         Debug.Log ("Obj B OnDisable");
     }
 
     private void Listener()
     {
         
     }
 
     private void OnDestroy()
     {
         Debug.Log ("Obj B OnDestroy");
     }
 }

Question :

1. When OnDisable in ObjBEventListener.cs gets called OnDestroy in ObjAEventHead.cs has already run it's course. So would there be any problem if I try to deregister in OnDisable, like I have done below. NOTE - It doesnot throw null reference exception.

2. For building large projects, what is the best practice?

Thank you, Karsen