Here is documentation which may help you:
There is no way to convert a commercial account to academic. There is a dedicated sign up form which checks if your email address is eligible for an academic account.
Ad1. Yes you can design a model without any attributes.
Ad2. You may change notation. Please see this blog post: https://vertabelo.com/blog/how-to-change-diagram-notation/
Ad3. There is no way to change how many details are displayed on the diagram.
We've prolonged you trial.You'll be able to delete these extra model.
We do not provide a desktop version.
user_group_type in Users and Groups and user_group_type in Software and plans are the same table. It is shown twice in the diagram in two different sections but both represenations refer to the same table in the database. We've used the table shortcut feature of Vertabelo. You can read more about table shortcuts here: https://vertabelo.com/blog/vertabelo-feature-shortcut-tables/
It is fixed. Please check if it works for you.
Customer support service by UserEcho
Since it's a public post I've redacted your comments.
Please make sure you provide the correct user and password on reverse engineer.