What can you do in Advanced Section of Look and Feel step in Pardot Form

LenoxSoft has a Pardot form on their website that adds prospects to their monthly newsletter list upon completion. Recently, they have noticed some of the prospects on this list have invalid email addresses.
What method should be used to only add valid email addresses to their list moving forward?

Choose required fields while creating a Prospect

How often does Pardot check for changes in Salesforce

What should be enabled on a Pardot form if an Administrator wants to sign many people up on the same computer at a trade show booth?