How can I only import or simply migrate content (nodes), related terms and users/content-authors from a D7 project into a better structured D8 installation, which is similar to the old project, but meant as a project upgrade replacement, but with changes regarding how things work in D8 and which require to import the data only, apart from the code/modules of the old project?
The D8 installation is already prepared to reflect the old project with the same fields, menus, etc, but it uses different solutions for relationchips than its D7 predecessor. I would love to import content, comments, terms and users seperately (for example as CSV) and with key-ids helping to rebuild their relationchips. But ...
TBH, the migration docs I read over the last days made me even more confused than being helpful since many little in between parts and steps are not further explained so that I can not hook into and alternate the steps for my needs.
All I already know is, that Feeds and Feeds import isn't ready yet and that migrating is rather complex and is made for not only importing content but for whole project structures? But how if so many modules have no D8 version or working upgrade path?
What I read so far is: https://www.drupal.org/docs/8/modules/migrate-source-csv/using-the-migrate-source-csv-plugin
which maybe comes close to what I maybe need for my issue. But I have a hard time to understand parts of it. So I see a use example with
migration_groups: - ACME import
in it but without explanation if this line is required and what it is about. Googling for migration groups confuse me even more.
Is migrate_plus with migrate-source-csv the right direction for my purpose and is somebody out there who can help about the terminology of the migration docs and what parts are important to understand?