Hey Holger,
1. that is funny. I need to investigate. Joomla should automatically pick whatever you've defined for the menu item as meta description.
2. I see. Well, I've intentionally disabled those buttons as I don't want the users to mess with them (one could use for example JCE to link to articles). Anyway if you want to enable that button in the frontend go to
components/com_hotspots/models/forms/marker.xml
around line 51 find this
<field name="hotspotText" type="editor" class="inputbox required"
label="COM_HOTSPOTS_FIELD_DESCRIPTION" description="COM_HOTSPOTS_FIELD_DESCRIPTION_DESC"
filter="JComponentHelper::filterText" buttons="article,image,pagebreak" required="true"/>
remove the article from the buttons section and it should appear.
For the backend -> just look for the file under administrator/same_path_as_above.
Cheers,
Daniel