Welcome to the Community, @MG9. I can provide insight for your setup questions. 

As to your first question, both you and your husband will be able to work at the same time and will be able to see the data as it's entered. For the second question, both of you can be working on the same file at the same time. The numbering will follow the sequence that you have set up and based on when the transaction was saved, so the numbers will be accurate.

Lastly, you are correct in that you will need a multi-user license to complete this setup. I'm including an article which provides an overview of setting this up: Set up multi-user network. 

I want to ensure that you have the optimum configuration for your business, so please feel free to let me know if you have additional questions. Have a wonderful day.