To get information about your mdi child forms like this, you really shouldn't be involving the tabbed mdi manager, which is basically just a component to allow you to layout your forms in an alternative fashion. You can just iterate the mdi children by using the MdiChildren collection I mentioned earlier. You can then count how many of a certain Form type are there.
That being said, you can handle the InitializeTab event of the tabbed mdi manager to set these properties on a tab when its associated form first opens. You can also get the tab associated with a Form by passing the Form into the TabFromForm method on the tabbed mdi manager.