Thank you for reaching out to the Community, pbel. 

Yes, you're correct. Creating a new estimate and new invoice is the best option to change the customer on your invoice. Once you change the customer in your invoice, the estimate that is linked to the previous customer will be unlinked.

I'll add this article for more information on who to customize your sales forms in QBO:  Customize invoices, estimates, and sales receipts in QuickBooks Online

After you process a payment from a customer, you can refer to our article in recording invoice payments in QBO to mark it as paid.

Don't hesitate to comment if you have more concerns about managing your sales forms. I'm always here to lend a hand.