The 'Family name Sans does not have an entry in the font lister error' may be a red herring: it's due to the default font in your preferences.xml file being specified as 'Sans', when you don't have a font by that name installed on your system. Can you confirm that at least that warning goes away when you edit preferences.xml? (replace Sans with 'Arial' or something... Preferences.xml should also be updated if you open a document, create some text using an installed font, then close Inkscape normally...
The 'Family name Sans does not have an entry in the font lister error' may be a red herring: it's due to the default font in your preferences.xml file being specified as 'Sans', when you don't have a font by that name installed on your system. Can you confirm that at least that warning goes away when you edit preferences.xml? (replace Sans with 'Arial' or something... Preferences.xml should also be updated if you open a document, create some text using an installed font, then close Inkscape normally...