I wouldn’t insert into DB directly. There are metadata fields that could be missed. Instead, write a script to convert TW data to Everdo JSON and then import the JSON into Everdo. If the import succeeds, then the DB is likely in the correct state. There are few mandatory fields in Everdo JSON, so mapping TW data projects and next actions should not be difficult. Post here if you run into difficulties.
Try creating a few items, projects and tags in Everdo, then doing a JSON export too see how it works.