Looking at the docs it seems like I just need to add to the config.json for the layout but not dice. There are 5 normally but I would like 7. Where do I control the number of widget slots?
You control this from the config within each layout. For instance, the default one like you said has 5 you can easily add two more like below.
If you add it to the themes layout default config.json then the next app you create after you restart WAB and you choose the billboard theme it will have your mods. If you want to add more place holders to an existing app that is using the billboard theme then you have to change to another theme (After you made the changes to the layout default config.json and restarted WAB) and save your app with that new theme and then when you switch back to the billboard theme your ne placeholders should be there.
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