I'm joining this thread so I can share some details about sending emails, bweiss.

Currently, only the tag “[Invoice No.]” and "[Company Name]" are available and can be added to the subject line. Note that the "[Company Name]" is for your business name and not for the client's company name.

As a workaround, you can manually enter the client's name or client's company name. When you click Save and send after creating an invoice, the Send email will pop-up so you can modify the email message. Then, select Send and close.

You'll want to check again the articles shared by my colleagues. It'll show you how to customize your sales forms in QuickBooks Online.

Keep on posting here if you need anything else. Take care!