Move from Wp to Drupal without downtime
Based on what you've mentioned, you will want to install drupal 7 separately and try Wordpress Migrate.

https://www.drupal.org/project/wordpress_migrate

It only needs the export of Wordpress which can be done in the Wordpress admin.

You will want to try this out first on your own machine, Acquia Dev Desktop will work for you. Read through some of the docs and walkthroughs on the migration. I've done it a few times, it's very quick and typically works fine.

https://www.acquia.com/products-services/dev-desktop

Once you are setup and established, you can migrate to Drupal 8.2.x-8.3.x without much trouble.