Building a ecommerce site that will have local delivery (But offering services nationwide), how can I build this site to rank organically and in local business results for individual locations around the country.

I am building an ecommerce site that will involve local delivery, but offering delivery everywhere in the country. A similar example would be an online store that sells flowers and they use a local florist to fulfill and deliver the order.

I am torn to create one site offering services nationwide or if I should create multiple sites that are based in a certain area? Having a site that services say Atlanta, GA, I will rank organically and for local business results if people are searching for services in Atlanta.

If I create one site that offers services around the country but will still have local delivery, is there a way to rank for local results? I would likely be using shopify. Is there some type of Plugin that could help me with this?