I’d love to help you but I don’t understand what exactly does not work as expected. What is $data what is the modulelist field. What has the code to do with the fact that you can only add one item (in the Panel, I guess?).
The custom list module displays only one input field (of the list) in the builder module. That means I can’t really create a list. I think it’s because of the builder plugin and I didn’t integrate it properly.
Should work, though. Once you add an item, a new input field should appear.
Make sure that your indentation is correct and better use spaces then tabs. Looks like you have mixed tabs and spaces and the indentation is also not correct if I copy the above code into a blueprint.