Well I almost spammed the forum 
Take a look. Maybe it explains more what I want. One thing, no core mods if it is possible. Maybe it can be used for a starting point. Thank you for your replies!
Can you send me your contact info @ cirsten@jeames.nl ?
http://forum.getkirby.com/t/hide-add-edit-panel-part-if-role-and-template-equals/590
&
http://forum.getkirby.com/t/help-for-the-php-newbies/965
&
http://forum.getkirby.com/t/create-page-via-the-frontend-with-file-upload/872