Upgrading Drupal

any suggestions?

Using the Updates tab (/lightning-8.x-2.12/admin/reports/updates/update) on my Drupal website to download Lightning 8x-2.13.

This error occurs:
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Downloading updates failed:
lightning-8.x-2.13-core.tar.gz does not contain any .info.yml files.
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Looking in /tmp the info.yml files are there

I have an idea and I wanted to float it by the community before I dive head first into it. Would it be feasible to gradually migrate to Drupal 8 from Drupal 7? My idea revolves around the Redirects 404 module, but I would have to attempt to port it to Drupal 8. The process in my head looks something like this:

Hi,
I have updated to 7.50 and received a number of warnings about missing modules. Most I have now fixed but this one ..
User warning: The following module is missing from the file system: ctm. For information about how to fix this, see the documentation page. in _drupal_trigger_error_with_delayed_logging() (line 1138 of /home/blatchin/public_html/includes/bootstrap.inc).
looking for the CTM module. I am having problems trying to find a D7 CTM module. Does such a thing exist? If so where, if not how do I resolve this warning?
Thanks

What would be causing the problem(s) below, and what is solution to fixing this dependency problem that should not exist?
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When trying to update to Drupal 8.3.2, the following composer command line utility error is produced:

When trying to perform a migrate-upgrade from a Drupal 6.38 site to Drupal 8.3.2, a migration is shown as created and visible under "Migrations" on the new D8 site, however, when trying to perform a migration on said group, I am only given the output "No Migrations found". When running 'drush ms' it does not show any current migrations at all, just outputs white space.
If I try to run migrate-upgrade on the same database, it tells me that "'migration_group' entity with ID 'migrate_drupal_6' already exists".