Enabling OG without denying access to 'public' for existing content.

Drupal 5.1
CCK, Date, Views, Calendar Views, ecommerce

1. First Question: Is OG necessary to create access permissions to content nodes? Meaning 'User Roles' do not allow control of access to content, and forum containers for instance. 'User Roles' only allow admin and configuration permissions, correct? So if I want to create content, Forum Containers/Forum/Topics for a specific group, I need to use OG?

2. Second Question - Problem: Upon enbling OG, all existing content on the site became inaccessible to the anon public, even though I configured default to allow 'public' access. Can I enable OG once I already have content and keep all content accessible to public' unless otherwise specified? Or do I have to go back to every node and select 'public' one by one?

3. Third Question - OG and Forums: It looks to me like the onlhy way to control access to forums is by topic, correct or no? Meaning is it possible to hide a container altogether from all but selected Group? Or does the container and the Forum have to be visible, and the user only sees the Denied Access message once they hit an actual Topic?

Thanks much, can't wait to get this working.