Hi Mike,
You can accomplish both of these scenarios by adding a DocumentLibrary grid to the preferred portal screen. You can use the session value for Portal - Entity to filter for only documents related to the customer who is logged into the portal.
If you’d like to make a few documents available to everyone, I’d suggest adding a custom yes/no field to the DocumentLibrary table for this (IsForPortalUse). This way you can build your filter to include all documents with a value of yes in the field for anyone. I hope this helps.
--Audisho