Welcome to the community @DawnTA 

No, a new form is not required when you enable double opt-in. The form works the same whether it’s single or double opt-in. That setting applies to the list, not the form. 

A profile is created when a user submits a form, however, with double opt-in, there’s an extra step - a click in the email confirmation - before they are added to your list.

You do not need to add any additional emails to your welcome flow.

I do recommend adding some copy  to your form’s ‘success’ step (after email submission) that tells them to check their email (including spam) and that they need to take action.

Also, review the double opt-in confirmation email for your list. Klaviyo’s default is quite basic, so you’ll likely want to update that.

I hope that helps, but if you have any further questions, please let me know.

Andy