Your expense report isn't added to your invoice till the invoice is saved—that means if you attach the report during creation and then delete a line item before saving, the report will correctly have that expense entry removed, as well.
Below the total you can include any additional information, such as a thank you or a reminder. - When you work out the contract with each client (and yes, you should have a contract in place!), you'll list out the terms of how often you plan to invoice and when you should be paid. For instance, you can agree to bill on the first of each month, or biweekly so you get paid every other Friday.