Hi Patrick,
Sorry to have kept you waiting so long.
I met trouble while I execute send email workflow, it always gives me error and thus notification email can't be sent while I using default onmicrosoft mailbox
Now I got success with add another mailbox as CRM email server (Gmail).
My implementation is that adding a custom two option field called "Is From Marketing Form" and set its default value to No in Contact entity Customization,
then I also add same two option field on marketing form and map it to the previous field, set its default value to Yes and enable "Hide field" option for it.
Result are below:


My customer journey setting:
Set your landing page as start tile, add a trigger to detect whether form submitted, finally add workflow as end tile.

The workflow can be simply configured with "If contact Is From Marketing Form equals Yes" and an "send email" action, new contact name will be automatically tracked with dynamic value.
Please check "As an on-demand process" option before activation, it will make the workflow be an available option in Workflow tile drop-down list.

Be aware of that once a workflow is added into customer journey to execute, Start when and Scope fields will be ignored.
Finally, you could read this thread for Gmail integration in CRM.
Regards,
Clofly