Everyone submitting a form with a Legal Signing feed that has a signing workflow enabled would have to be a signer, the initial person that submits the form is always used as the first signer that kicks off the signing session. You can’t have a submitter that is not a signer for that form when a signing workflow is enabled.
If you need an initial submitter to kick off a session but not have them be a signer, you’d need to chain together multiple forms to do so. e.g you have one form that is submitted by the non-signer and they provide at least the email address for who will be the first signer in the workflow for the second form. That first form has a notification that is sent to that first signer’s email when submitted with a link to where the second form is embedded where you’ve set the workflow up, passing any other necessary data through from the first form with dynamic population. The first signer would then submit that form kicking off the actual signing workflow.
Every signer is automatically served the Legal Consent field on a form where a signing workflow is enabled and must check the consent checkbox before submitting as collecting explicit consent to sign and do business electronically is required to be compliant with US e-signature law.