How difficult is it to create a modern website and what can I need besides a website for e-commerce?

I know that creating an online store is quite difficult, despite the number of site builders there are. I know that you can use ready-made templates and themes Shopify and Magento. But still, you can get some functions only if you use additional software, for example, I use this powerful analytics tool https://www.savvycube.com/magento-analytics to get more statistics about my online store. This helps me to control the effectiveness of my advertising, to check what visitors of my site are looking for, to ensure that I have the goods in stock and to make changes to the navigation of my site depending on the needs of my customers. Setting up such software doesn't take much time, moreover, this program has an affordable price, but all the advantages of this program are difficult to describe. It’s really cool that you can use these tools to have accurate data and you don't need to change the structure of yoursite.