Email addresses and Adobe Muse BC basics

I understand that the "free" hosting is BC basics. Doesn not include emails.

However, I want to take advantage of the free hosting for a customer, but she needs an email address or two obvs.

So my question is. Do I pay for the email only hosting with the ISP with whom I have the provider, and if I do, how does this work in conjunction with the BC hosting, once I have reset the DNS nameservers?

And if I want to upgrade to BC Basics+ which I believe will give me 5 email addresses, will I only be charged the difference?

Thanks for your help with this!