Hi there,

500 error is usually server related, perhaps increasing php parameters max_execution_time and upload_max_filesize will help (you can ask your hosting provider about that).

I'm attaching the zip file though, you could also import stuff separately with this.  It contains a .dat file for the Customizer, .xml file for WordPress Importer and a .json file for Widgets. The latter can be renamed to .wie and imported with this plugin.

Hope this helps