You can create an invoice in the program without a client's email address. However, sending it requires you to enter a valid email address. I'd suggest printing the invoice and manually send it to your client.
In line with this, I'll take note of your feedback and submit this to our product engineers. They can evaluate your preference for future releases. I recommend checking out our QuickBooks Self-Employed (QBSE) Blog to learn more about our product innovations.
For your second concern, yes, you can change the format of an invoice. This can be done by clicking the Customize button at the upper right. I'll guide you how.
Go to Invoices from the left menu.
Locate the invoice.
Select Edit in the Send drop-down from the Action column.
Choose Customize at the upper right.
Click either Invoice details, Payments, Design, or Email to make any changes.
You can select Preview to review the changes.
Save the customization.
The screenshots below show you the first to sixth steps.
As always, you can go back to the Invoices menu. From there, you can duplicate, print, delete, and export the invoice as PDF from the Action column. For more information, see the For you section through this article: Invoices Overview.
Please know that I'm here anytime you have other concerns. Have a great day, @cassmcp1.