I am trying to create a directory site. The plan is to initially import all the directory submissions into Types then assign a user to a particular directory item and give them front-end editing access with a CRED form to just that one submission.
For example: This is a directory of 82 schools. I will import all the data for each school into Types via a CSV file and WP All Import plugin. So then I will have 82 unique directory posts - one for each school. I need to then assign a unique user from each school to each of those 82 posts so that each school can edit their own directory post after the initial import and into the future.
For both you will need to create the users that are going to be assigned to manage the school listings.
One way is to make the users the authors of the post. If you had a "My school" page then you would display the school for which the author was the logged-in user, which would also display a link to edit the school details. You might want to use a wpv-conditional shortcode (https://toolset.com/documentation/views-shortcodes/#wpv-conditional) to only display the form if the author and logged-in user match to avoid anyone trying to access the form directly from the url bar.
Yes, you should be able to import any standard WordPress post field (including post_author) as well as custom fields.
But you will have to have created all of your users first. You can't assign them if they don't exist, although you would have the same problem if you were using a custom field to denote the user managing the school.