@tharkos: Thank you!! That was the last missing puzzle. As of 10.03.2014 the plugin works.
As a reference for others:
First hiccup was understanding that Facebook Page UID needs to be a number you find out by adding graph instead of “www” in front of facebook.com. It looks like this “id”: “130821973783” for the Facebook page https://graph.facebook.com/gwup.org?fref=ts
The second was changing to the strtotime code posted here. My starttimes from facebook looks like this. [start_time] => 2014-05-29T14:00:00+0200 … I bet thats why we need the string to time conversion.
Third
Add
$args[‘Organizer’][‘Organizer’] = $event[‘host’];
to about line 145 to have the host added to the post.