We also talked in a workshop session (in French) two days ago about using Paratext Lite for community feedback. You could create a generic Paratext user, but they would have to be observers on the project, so couldn’t insert comments in the text. Any users you would want to give Reviewer status in the project (to be able to insert comments) would need an individual user (with no organization) created for them. Do a Google search for “Paratext Lite” for more info.
Another possibility would be to create a Scripture App (with Scripture App Builder). It’s possible for reviewers to insert notes in the text, and they can then send a file with all of the notes they have created to an email address that you can embed in the app. If it’s text being reviewed, you should probably put an expiration date on the app, so people can’t keep it too long.