Optimize Joomla Website

We have Joomla e commerce Website using Enmesse Component, with some customized modules, the issue is, most of these modules are using same image size as the one display on product details, this make website to be heavy (home page is 24MB). Seems that enmesse is creating thumbnails but same size as product image, which make it to be very heavy. Main task are; 1. Make En Masse to be PHP 7.2 compatible 2. Change thumbnails size to be as small as possible 3. Perform any optimization to make website as faster as possible 4. Perform any security patch to En Masse (because we have done a lot of modifications and Developers do not support it anymore and seems to have some security issues) 5. Change Map API because En Masse component is using old one