Creating a window to get user's textures for a tilemap.

I'm trying to make a window to support multiple texture entries by user. The user select a texture or drag one and click on "add" button, the texture should appear down the add button or something like that.

However I'm stucked, no idea which classes and tuts should I follow to accomplish and finish it. My current screen is like that:

I have created a class that extends EditorWindow and implements some OnGUI elements:

         private Texture2D _texture;
         private static int _y = 0;
 
         [MenuItem("Component/TEMP1/Create Texture Pack")]
         public static void Init()
         {
             var window = GetWindow(typeof(DwarfTexturePack));
             window.title = "DT2D Texture Pack";
             window.position = new Rect(30, 30, 400, 200);
             window.Show();
         }
 
         void OnGUI()
         {
             _texture = EditorGUI.ObjectField(new Rect(3, 3, 200, 200), "Add a Texture", _texture, typeof(Texture2D)) as Texture2D;
 
             if (GUI.Button(new Rect(5, 60, position.width - 5, 20), "Add Selected Texture"))
             {
                 if (_texture != null)
                 {
                     _y += 100;
                     EditorGUI.PrefixLabel(new Rect(10, _y, 200, 15), 0, new GUIContent(_texture.name));
                     EditorGUI.DrawPreviewTexture(new Rect(10, _y + 5, 100, 100), _texture);
                 }    
             }
 
         }

I would like to implemente something like that:

Which classes should I take a look or a tutorial that covers this aspect whould I learn?

Thanks in advance!