Is there a way to configure existing fields to be required fields for applicant input?

4. Is there a way to configure existing fields to be required fields for applicant input?  If so, how?

Yes, all you need to do is to go to the edit mode of your form after logging into your JotForm account at www.jotform.com, then simply:

1) Go to MY FORMS.

2) Select your form, and click on Edit form.

3) Select the field you want to required and enable the Required button:

If you need anything else, please open a new thread, we will be glad to assist you.