Custom field for the customer VAT number

A European client requested our invoices display their VAT number. So far we have two questions:

    1. Where do we store the VAT number? A custom field I assume.
    
    2. How/where do we expose the VAT for maintenance? The Customer form I assume.
    
We are searching for suggestions about an approach/implementation for this request.

Thanks for help and ideas. As you can tell, we are learning Acumatica as we go.

Tom Morris