Great start! It would be even better if when running the tool it took into account the structured data on the page that is already there. i just tried it on a page where I have JSON-LD for a local business and while the tool shows all the fields I should be using it has not picked up the JSON-LD in the page already.
Thanks for your interest in the Schema.dev builder. Please submit your ideas, questions, thoughts and requests for help with any specific use cases here! Looking forward to making Schema easier for everyone