In Orchard CMS I know that permissions can be set for content types. What is the suggested way to set permissions on single instances of content items. In particular, I would like to use the custom forms module to create multiple custom forms where some are only available to authenticated users while others are available to anonymous users. I am fine with creating a custom module for this but would like to have at least a general idea of what would is involved with building more granular permissions at the content item level. Thanks.
You can achieve that with the built-in Content Item Permissions feature. This enables you to attach the Content Permissions content part to your content types, which will add a set of checkboxes to the editor to customize the accessibility of each content item of that type.