Hi Tony
The reason I'm looking to do it from scratch is that its a case of "once bitten, twice shy".
This CMS will be replacing a Joomla based CMS.
I can't quite say I'm enamoured by the option of trading one "baggage included" opinionated CMS for another. Also in this day and age, removing the excess baggage means an improved security footprint.
Laura, fair enough.
At the time i used a static site generator (SSG), which was Jekyll at the time, to generate our website.
I could have used Joomla or Wordpress as the CMS, but these are terrible solutions as you mentioned, as they are not designed as pure CMS engines, especially for use with a static site generator.
I went with my own rolled CMS as well.
One part of my requirement was for a product sales database, which ended up being a lot more complex than your design, as I needed categories, product groups, products, prices by area and more. I did this in Postgresql, and pulled the data via a GraphQL API implemented via Postgraphile, which generates a GraphQL API from a Postgres schema automagically.
The other part was for the static web pages. What I came up with was to store pages and then a set of tags where I could assign content to each tag for the page.
For example, you talked about Page Headers and PageMainLeft. I stored these tagged with the name of the page, and the tag name, plus the content.
The SSG then saw the tags in the HTML page template, and pulled in the content via Postgraphile.
At the time I looked at several 'headless' CMS engines, and Strapi came close to meeting requirements, but was still in early development stages.
Today, I would look at a different route, likely leveraging something like Strapi. I may still consider using native Postgres tables to manage the product database, but there are a lot of other proven CMS options on the market now without the baggage of Joomla, Wordpress et al.
Node.js I regard as a necessary evil if you are developing relatively complex websites, integrating multiple APIs and other resources.
Very much depends on your environment though.
For example, one huge advantage of the headless CMS options is that the whole user management and access is built in if you have a large user base maintaining different parts of the website content. Another is things like formal APIs to get content, and access management / security of the content itself.
There isn't really a one-solution-fits-all-requirements option when it comes to content management, unfortunately.
Regards