So you are asking, how do you get your page content into a WYSIWYG editor?
Usually, you have that as a property on your Page model, where you store the html, then in the edit/create page you have your WYSIWYG editor connect to a textarea field, you store that in your db, then when you edit, you set the property as the value of the textarea and have the WYSIWYG connect to the text area again.
I've done this many times.
Also, there is not a WYSIWYG that is going to automatically handle file uploads into your Laravel app. If there is, I am unaware. Most likely there might be one that has the majority of this built in the front end side, but you will most likely have to handle the upload yourself.