Yes, we support the Confluence Cloud Migration Assistant. See Server to Cloud Migration for more information.
The Easy Dropdown Menu uses the following scopes: READ, WRITE, ACT_AS_USER, DELETE and SPACE_ADMIN. For a more detailed description of the levels of access, you are welcome to read this page from Atlassian: Scopes for Connect apps.
No data is stored outside of the Confluence Cloud. We use a confluence space that is private to EDM on the instance to store the data. An administrator of your instance can give himself access to this space if needed.
Yes, the Easy Dropdown Menu is only manipulating the look and feel of data within the Confluence page based on Data stored inside Confluence.
You can find our End-user license agreement here Easy Dropdown Menu - Cloud.
This is due to a limitation of confluence connect addons. Each macro is an iframe and only 20 iframes are allowed to load in parallel. Here is also a link to our documentation about bad performance with a large number of EDM Macros on single pages: Known Issues.