Let me address your concern about changing the format of your estimate and invoice when sending.
The way to have this feature available to you is to create or edit a custom form style for the Estimate and Invoice.
- Go to the Gear icon at the top.
- Under YOUR COMPANY, choose Custom form styles.
- Click on the form you would like to change or create a new one by clicking New Style.
- Select the Estimate or Invoice option.
- In the Design tab, tap Change up the template to change the layout.
- Tap the Content tab to customize the information you want to show in the template.
- Choose the Email tab to personalize and change the message customers see when they get their estimate or invoice.
- Hit Done when finish.
After performing the steps above, ensure to select the template you've customized when creating an invoice or estimate by clicking the Customize button at the transaction page.
To learn more about how you can personalize your sales forms, visit this link: Customize invoices, estimates, and sales receipts in QuickBooks Online.
If you'd also want to import your customized template, take a look at this article: Import custom form styles for invoices or estimates.
For your future task, you may find this great resource helpful: Convert an estimate into an invoice in QuickBooks Online.
Please let me know if you have other questions. I'd be glad to help you further.