Email forms in popup format

Can I create an email form in popup format on the home page that only shows up once?

That is indeed possible. To do so, you will first need to have a lightbox form. Here's a guide on How to Create a Lightbox Form. Once you have that lightbox form, you can then follow this guide on How to Automatically Open or Load Lightbox Form Based on Cookies Using Javascript. By doing so, your users will only see the lightbox form on their first visit to your page. If they refresh the page again, then the lightbox will not appear anymore. 

If you need further assistance, please let us know.
Regards.