I have a library with client documents with client account numbers, and another list with client information that contains the account number, household number, client name, etc. Some client account numbers have multiple household numbers associated with them. In my documents library, wherever there is a document with a specific account number I'd like to pull each household number into one (or more) fields, just to have them there for reference. Would a multi-value lookup field be the best way to do this?
You can have a household information in a different list as you mentioned and add a multi-value lookup column to the client documents library. This will create one to many relationship.