www.wysiwygwebbuilder.com

is there a way to add CMS / Forums where the clients can post topic as well lock it up?

A forum is a script that you will need to install on the server.

WYSIWYG Web Builder has built-in CMS functionality:
https://www.wysiwygwebbuilder.com/cms_tools.html
https://www.wysiwygwebbuilder.com/editable_content.html

But you can also integrate third party CMS solutions:
https://www.wysiwygwebbuilder.com/cushycms.html
https://www.wysiwygwebbuilder.com/surrealcms.html

ah, will there be a ext for this in the future ??

You may want to consider looking at phpjabbers scripts for your needs. They are easy to integrate into WB and offer backends for your clients.

https://www.phpjabbers.com/php-forum-script/

If you want a full forum, you could use the free phpBB which is the one this forum uses.
https://www.phpbb.com/