Study Bubble’s ecosystem. Their plugin market is a failure for this reason.
Strong curation and testing by Adalo is essential.
If you don’t enforce strong documentation & testing standards, most plugin makers won’t provide it.
Worse, your forums - like Bubble’s - will become littered with complaints about the plugins, error codes, useless responses from the component makers, and more. Over time, even most plugins that initially work end up failing as the platform or (3rd party dependencies) change - and the plugin providers don’t stay out in front of the changes.
I am a bit dismayed to see one of the worst offenders on Bubble - a company that makes lots of plugins for Bubble that don’t work, throw errors, and more - is now in Adalo’s plugin ecosystem. 
Please take a very very strong role in making sure this marketplace works. Just opening it up and hoping it works out will fail.
After 2 years of saying they would no longer build plugins, guess what Bubble is now doing again with a vengeance? Yep - building plugins. Because the marketplace is a disaster.