I want to switch to sending emails via authentication and using TLS. I tried the send notification workflow and with setting the STARTTLS to true and putting in the other info it works.
Is there a way to set STARTTLS as a default or will I always need to pass that as a parameter when preparing my message as part of my workflow?
You can copy that workflow, modify the scriptable task to make TLS default. Than use your modified workflow.
A less invasive option would be to create a new wrapper workflow, that will internally invoke the original 'Send notification' workflow using the workflow element item.
This wrapper workflow should expose only a subset of original workflow's input parameter. The other inputs that you want to be hard-coded (useStartTls and useSsl) should be created as attributes with default 'true' value in the new workflow and bound to the corresponding inputs of the inner workflow.