Rob,
Welcome to the world of software development. I don't believe your question is specific to Node.js, but could be implemented in many different languages/frameworks. There are already many platforms where users can create websites for different purposes. Wordpress.com is one example and is typically used for blogs. Wix is another that's more generally used for small business sites. SilverStripe, Ghost, Joomla, Drupal, Keystone ... There are so many CMS systems available I would hesitate to say the world needs another one. Maybe you have some specific vertical in mind where your new hosted site platform would be better than the available options?
If you're goal is to learn more about programming by solving an interesting problem and building a product, I'd urge you to swing your ambition-hammer a little harder. Building yet another CMS will be less fulfilling than looking further afield. Even with no money and only your own time, there are many exciting projects to explore and dents to be made in the universe. How about: FPGA-accelerated javascript? Portable multi-cloud Lambda function tools? Workaround for Domain Fronting in DNS-filtered countries? Homomorphic encrypted databases? ISM-band peer-to-peer off-grid communications (networking with radios; not the internet)?
You said you're just starting this journey. Please fail at something hard rather than succeed at something easy. You'll learn a lot more and maybe you'll make the world better.
Best
Mikkel,