We found it very tedious to incrementally upload additional images. We asked the development staff and they created a module, quite inexpensively, that allows bulk uploading of additional images and does a fantastic job. You can see the results at www.dangelointernational.com, but you need to click past the splash page and drill down to a specific product.
Before, when we were adding images through the administrative back-end, we would wipe them out when we bulk uploaded our products with a refreshed database. Now it is simple to stick all the images in a directory and upload a csv file for the products with the detailed image and another csv for additional images. Works great!
I don’t know how cs-cart handles their add-ons, but I’d sure ask them about it if you have a lot of additional images.