Hi Owen, glad it was somewhat helpful. With any solution there's always gotchas!
On your other questions:
- Backup and restore
- Bulk updates
- Resource management and task dependencies across multiple projects
For backup and restore, there's good news here. While it's not possible to backup the Default environment and it's data specifically, if you work with your IT group to setup a 'named' environment of Planner and the Power App, that database can absolutely be backed up and restored. There's even the ability to move the solution configuration between environments if you intend to do a prod/dev setup.
For bulk updates, maybe if you share a bit more about what you're looking for here, we can come up with ideas/options? In the end of the day you are writing back to a database, so understanding the specific use case would be helpful.
For resource management, that's definitely possible based upon how the Planner Premium scheduling engine works. Alot of that happens via the Power App and Power BI reporting, here's a link to a webinar covering this specific topic and the solution's capabilities: https://youtu.be/6eZIzN211cA?si=63OBAuEu3CBEKVJW
If you need more than what this offers, the Project Online solution is available, which gets to a much more granular resource management level (timesheets, % allocation on activities, resource requests, etc.)
Finally on task dependencies between across multiple projects, you are correct, this is currently a function that Planner Premium does not support, mainly because there's no way to open multiple plans simultaneously and create those linkages. That's another thing Project Online and Project Pro do really well, so if this is a requirement, that solution may be a better fit.
Reach out or direct message me if you'd like to have an offline conversation about any of this. Thanks.