Group Based Licensing is currently in preview, so keep in mind this answer could change. Today, in the preview, you just need to have an Azure AD Basic subscription available in your tenant. Users do not need to be assigned the Azure AD Basic license to use the Group Based Licensing feature. The administrator who configures it however should be licensed.
Dynamic groups on the other hand require Azure AD Premium P1 licensing for any members of the group.
Oh I'm sorry, I missed the dynamic group piece. Yes, dynamic membership requires Azure AD Premium for every user that is a member. I've seen it not enforced, but it's still a rule I'd recommend abiding by to stay in licensing compliance.