Upgrading 7 to 8

Hi so I have read the documents Drupal 7 to 8 but I have questions and errors about migrating from Drupal 7 to 8. So here are the steps I take to try and migrate, maybe someone can help spot where I go wrong:

  • Set up blank Drupal 8
  • Enable Migrate Modules
  • Import D7 database and public files
  • I get warning that I am missing 72 missing upgrade paths but continue

Once I get to the main page, my content has been imported but my subtheme (a bootstrap subtheme) is missing, along with my template files, css, and js. When I try to upload bootstrap theme and install it I get an error:

“DrupalCoreConfigPreExistingConfigException: Configuration objects (bootstrap.settings) provided by bootstrap already exist in active configuration in DrupalCoreConfigPreExistingConfigException::create() (line 65 of core/lib/Drupal/Core/Config/PreExistingConfigException.php).”

Is there a different approach to upgrading? Willing to use Drush instead of the UI. And how to I transfer over my subtheme?

Thank you in advance!

Drupal version: 

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