Hi Kurt,
First of all, you are making perfect sense. Secondly, you are in the correct place for your question, we ask that you do a search on the forums and view our documentation, including the Webinars and if you still can't find the answer you are looking for, then create a forum thread. The benefit now, is that if someone down the road using Method had the same question, your thread will be here for them to find.
You logic is sound, my suggestion would be to build a new screen based off the Customer table (this will give you the Dropdown for the Sales Rep, after allowing the grid to be editable), and mimic the original CustomerList Screen as much as you want, if you log in as two different users with full permissions at the same time, you can compare the two screens. Hopefully this will help you get going with the setup you are looking for. If you have any further question based off this information, just ask and we will try to offer more suggestions. Note, you could also base your new screen off the Entity table (as you saw, it holds these values as well), however it would give a list of everyone in your databse, not just your contacts.
-Ben