So… yes to the structure. That’s exactly right. But JSON is not necessary with Firebase (it can be used).
You simply use the “Set Cloud variable ‘name’ block” and enter the path to the value as the name of the variable. I can provide a screenshot of blocks later if it’s helpful but you might do something like group name/Variable to get the value in 1. A. above. If you had unique names (which you’ll want to use), you might have this:
A. Miata: 14
Maybe the 14 represents the number of Miatas that have been retrieved from the JSON response. Not a great example, I know, but bear with me.
Your Cloud variable would be named [bucket name]/Mazda/Miata. There’s no need for the realtime DB blocks. You just use variable blocks and that’s it.