First up, welcome to Method!
If you're familar with SQL then you should be happy with the customization possible in Method - we are SQL based. You can add new sales reps in Method under the QuickBooks tab group > Lists. There are some limitations from the QuickBooks SDK which is stated at the top of this page:
Due to a limitation of the QuickBooks Software Development Kit, you are only able to create new Sales Reps through Method. If you'd like to edit or delete a Sales Rep, you'll need to do this in QuickBooks.
Post back if you have any other questions,
~C