when you run the security assist wizard, go to the Manage Pages tab. Click the pencil Icon next to Change Field Settings to change the validation requirements. this will allow you to set the minimum number of character for the fields in your registration form.
to edit this after the pages are created, select the field in design view, then click the blue bounding box, this will open the spry validation settings in the Property inspector.
The UserGroupID column should not be included in the registration form, when running the security assist wizard, you should edit the registration page to not include that field. In the database, that field should be set to have a default value of the lowest user group.
the css file that sets styles for from elements is located here:
see the following roadmap article for details on styling forms with css: