Should I get as much of the supply chain in my business?

As a general rule, yes. But it also depends on what you sell. There are businesses that sell goods online without having bought anything. They sell what others have on the shelf and focus on marketing through a webshop. With a quality partner that can work very well. These businesses own a minor part of the supply chain but have solid contracts with others within the supply chain. Others who work like this and offer services are AirBnB and Uber for instance.