Hi! My name is ***** ***** I'd love to help you with your question.
My understanding is you are asking if you create a distribution list in Office365, does that count as a billable email address for the Office365 service, is that correct?
Assuming my understanding of your question is correct, it looks like there isn't an additional cost for that because you are paying for the mailboxes that the distribution list will forward to, and so there would be no extra fee. I'm trying to find a page on Microsoft's website to prove that, but I wanted to give you what I found so far.
I apologize, but I'm unable to find a link to provide you, but I have found several sites describing the situations you seem to be asking about. Groups will possibly incur extra cost and have some admin considerations. If you only want to have an email that forwards to other emails (distribution list) and you don't send for it, that should be covered at no additional cost.
If that answers your question, great! In that case, I would really appreciate it if you would kindly rate my answer. If you have further questions or are unhappy just reply here instead and I will try to help you!