Can I add a custom dialog, on the image link popup, to show the images already in my website.
Yes, this feature (option to open custom dialog) is still in development (95% complete). Using the current 'direct image embed' also allows embedded images to be saved on specified path on the server.
Another question, how flexible it is, for uploading new content blocks?
I also dint find any email address or any contact info, in your website.
Could you also have some kind of trial, so people may try, before they buy.