Performance optimization for custom class in ScriptableObject

Having read about Custom Serialization in the docs I am left wondering if I should be using custom classes inside of ScriptableObjects.

For example I have an SO called ItemState that holds a list of of another SO:

Code (CSharp):

1. [CreateAssetMenu(fileName = "State_Item_StateName", menuName = "ScriptableObject/States/ItemState")]
2. public class ItemState : ScriptableObject
3. {
4.     [SerializeField] public List<EventBase> Events = new List<EventBase>();
5. }

So has its own classes, for example:

Code (CSharp):

1. [SerializeField] public ItemState NextState = null;
2.     [SerializeField] public SpreadsheetData[] ReactionsEventMessages;
3.  
4.     [HideInInspector] public int ItemID { get; set; }                    
5.  
6.     [System.NonSerialized] public ItemStateManager ItemStateManager;

For the classes that don't need to be serialized I have added the NonSerialized attribute. However, I am wondering if my approach is generally wrong.

Would someone be able to tell me if I am using SOs incorrectly? I love the modular approach, but am concerned that I'll be taking a performance hit or is it just increased build times?