What backend are you using?
The NodeBB app uses mongodb.
For example, CPU, memory, disk?
By default, the app is configured to use 300MB RAM. But this is tunable with a UI depending on the traffic you get https://cloudron.io/blog/2016-09-08-release-0.20.0.html. The Disk and CPU depends on the server you install NodeBB on.
How is NodeBB Co figured (redis, mongo)? Do you get admin control on the hosted plan?
Yes, you get admin control.
I want to clarify that we are not a managed NodeBB provider (if you want that, it's probably best to get it from NodeBB itself (https://nodebb.org/pricing). Instead, the Cloudron is a platform that makes self-hosting easy. We automate updates, backups, dns/ssl management etc. You can run the Cloudron platform on your own servers or get a server from us. Think of this as a very highly optimized ubuntu for web apps.