Hi,
A. Is my basic view of what Metabox can do right?
The plugin only does the job of creating meta boxes and custom fields in the admin area. It doesn't handle the automatic showing the custom fields values in the frontend (because it depends on where you want to show them or how you want to use them).
I think it's half of what you want.
B. How do I get the customer fields visible in the frontend?
Please follow this documentation: https://metabox.io/docs/get-meta-value/
This was the text of the notice with the fatal error:
Can you give me more details on the error?