I have to admit that I’m still struggling a little with the Online Editor as well. That’s not because it doesn’t work well, but rather because the “App CMS” came first and the “Online CMS” was added later.
For my projects, I often use fairly extensive YAML frontmatter structures with multiple nested levels. With the App CMS, it’s possible to build a very clean, well-structured and maintainable frontmatter setup – and many of my existing projects are already built around this approach.
With the Online CMS, however, I sometimes run into limitations. More complex and deeply nested YAML structures can’t always be recreated in the same way. In many cases, you can only go so far with nested levels.
So, if you decide from the beginning that you want to use the Online CMS, you may need to take a different approach when designing your frontmatter. The data structure often needs to be considerably flatter than it would be in a project primarily managed through the App CMS.
That doesn’t mean that the Online CMS is necessarily less powerful than the App CMS. In my opinion, the real issue is the enormous flexibility of the Elements CMS. On the one hand, that flexibility is one of its greatest strengths. On the other hand, it can sometimes lead to a certain lack of consistency between the different options and workflows.
At times, I’m missing a clear and consistent path for how certain things should ideally be implemented. I hope you understand what I mean.
That’s why my current recommendation would be to decide as early as possible which route you want to take: Online CMS or App CMS. Especially with larger projects, I think it makes sense to make that decision before building a complex frontmatter structure.
As for providing an example project for the Online CMS, I think we may have to wait for another CMS update. At least at the moment, I don’t see a really practical way of sharing a fully preconfigured example project.
The main problem is that, as far as I know, the configuration of the frontmatter fields in the Online CMS currently can’t simply be exported and then imported into another project.
Since every user first has to install the Online CMS themselves, they also have to manually create and configure the required fields after installation. So at the moment, an example project would only provide part of the required setup.
My feeling is that the Realmac team has probably already recognised this issue, and perhaps we’ll see an update addressing it later this year. Ideally, once you’ve configured your frontmatter fields, the configuration wouldn’t just be stored within that particular Online CMS project – you’d also be able to export the complete field configuration and import it into another project.
And since I’m pretty sure the Realmac team is reading this, I’ll just add: the competition already has this feature. ^^
So, for anyone who wants to use the Online CMS right now: have a look at Ben’s instruction video. It actually explains pretty much everything you need to know, although Ben goes through some of the steps rather quickly.
Maybe our moustachioed guys will follow up with a more detailed tutorial at some point. 
And otherwise, just ask here in the forum. That’s what it’s here for.