Hi,
I have gone through your requirements for changing your sites cms from Joomla to another CMS, i would suggest Wordpress as it will be more secure and more user friendly.
Having extensive experience using WordPress to design and develop ecommerce site, multivendor portal, education websites, and LMS portals etc in Joomla and WordPress etc, I can deliver top quality results for your CMS.
My portfolio have the links to my most prized development works, please check anf let me know your thoughts.
I will creating the new CMS with customizations to provide all feature from Joomla site. The data will be transferred through scripts.
Please come on chat, so we can discuss your requirements in detaul.
Regards,
Mir