
Hi @dehmos27,
You can't embed a model-driven app on Power Apps Portal. You actually build Portals forms with model-driven form designer, but these forms are rendered differently on Portals to Portal type forms. You can embed a canvas app however (link below). As for your access question, yes local accounts can perform CRUD operations on CDS data. You have to configure Entity Permissions with Web Roles to configure the security and ensure external users have only access the the data that they're supposed to. Here a a few links to help with your questions:
Hope this helps!