I am not sure of the answer to your styles question but Lopocon is. When he sees this I am sure he will reply.
As for the Font and size toolbar options, you can remove them from the menu in the fckconfig.js file that is located in the Custom directory of the provider.
If you are using the defined DnnDefault menu:
FCKConfig.ToolbarSets["DNNDefault"] = [
['Source','Preview','-','Templates'],
['Cut','Copy','Paste','PasteText','PasteWord','-','Print','SpellCheck'],
['Undo','Redo','-','Find','Replace','-','SelectAll','RemoveFormat'],
['Bold','Italic','Underline','StrikeThrough','-','Subscript','Superscript'],
['OrderedList','UnorderedList','-','Outdent','Indent'],
['JustifyLeft','JustifyCenter','JustifyRight','JustifyFull'],
['Link','Unlink','Anchor'],
['Image','Flash','Table','Rule','Smiley','SpecialChar','PageBreak','UniversalKey'],
['Style','FontFormat'],
['FontName','FontSize'], <- Remove this line
['TextColor','BGColor'],
['FitWindow','-','About']
] ;
Currently there is no official documentation. We are looking for someone to work on that.