Advanced Techniques:

1) How can I embed the customizer?

You can embed the customizer to another control, but the form of this control cannot be modal or the drag & drop will not work.
You also need to close the customizer explicitly by calling the Close method.

SpTBXCustomizer1.ShowEmbedded(Panel1);

2) How can I store more options related to the items customizations?

To load and store your custom data use the OnLoad and OnSave events:

procedure TForm1.SpTBXCustomizer1Save(Sender: TObject;
  LayoutName: String; ExtraOptions: TStringList);
begin
  // Save the Form's font size
  ExtraOptions.Values['FontSize'] := IntToStr(Font.Size);
end;

procedure TForm1.SpTBXCustomizer1Load(Sender: 
TObject; LayoutName: String; ExtraOptions: TStringList);
var
  S: string;
begin
  // Restore the Form's font size
  S := ExtraOptions.Values['FontSize'];
  if S <> '' then
    Font.Size := StrToInt(S);
end;

3) How can I store more options related to a specific layout?

The layout is just the position and visibility of the toolbars and dockable panels, but you can store more options related to a layout.
To load and store your custom data use the OnLayoutLoad and OnLayoutSave events:

procedure TForm1.SpTBXCustomizer1LayoutSave(Sender: 
TObject;
  LayoutName: String; ExtraOptions: TStringList);
begin
  // Save the Form's WindowState
  ExtraOptions.Values['MyOption'] := IntToStr(Ord(WindowState));
end;

procedure TForm1.SpTBXCustomizer1LayoutLoad(Sender: 
TObject; LayoutName: String; ExtraOptions: TStringList);
var
  S: string;
begin
  // Restore the Form's WindowState
  S := ExtraOptions.Values['MyOption'];
  if S <> '' then
    WindowState := TWindowState(StrToInt(S));
end;