Just a bit of a sense check - if I wanted to show the percentage of sales for this month that are unbilled (based on amount) is there a way to pull that out or will it require scripting?

Pretty sure you can do this with a saved search on sales orders and leveraging the ‘amount unbilled’ results field vs the total amount. You might run into wrinkles based on whether 100% of your sales go through sales orders or if you also have cash sales or direct invoices but that’s where I’d start.