Hello @gsgriffin,
I'm glad to see you reaching out to us here in the Community. Allow me to chime and provide additional information about customizing an invoice in QuickBooks Online.
There are specific fields and custom fields you can remove from the form. I agree with the steps provided by @Cummings2 regarding how to remove unwanted fields on invoices (see screenshot below).

You have the ability to remove fields from the Gear icon within the invoice or the Content tab (template customization). If the Sales Rep and other fields are added as custom fields, you can also remove them by editing the template.
Here's how:
- Open the invoice.
- Choose the template, then select Edit current.
- Go to the Content tab.
- Click the Pencil icon in the upper-right corner.
- Press Manage custom fields.

I've attached a link you can visit if you want to know more about setting a default custom template in QuickBooks: Customize invoices, estimates, and sales receipts in QuickBooks Online.
Drop me a comment below if you have any other questions about entering sales transactions or managing templates. I'll be happy to help you some more.