sharing_get_file_metadata access error

That endpoint only supports the "Team Admin" mode for "Dropbox-API-Select-Admin", meaning it "can access content of team folders and team spaces but not the team members' home namespaces". So, to be able to call that for files not in team folders/spaces, you'd need to use as_user with the relevant team member ID instead.

By the way, you can check the type of an object directly, e.g., to see if an entry is a FileMetadata, using instanceof like this.

Also, be sure to implement the pagination methods where applicable, to make sure you get all results, such as team_namespaces_list_continue and files_list_folder_continue.