A: Hello

A. There is a integration with WP, Ghost is not on roadmap now. When we have some demand happy to work on that, but there are so many headless CMS that you can merge with NEURON using API.
B. You mean for Ghost, nope. But we can work on that when we work on another integrations.
C. Post fields are defined in API endpoints:
https://neuronwriter.com/faqs/neuronwriter-api-how-to-use/

Hope this helps ;)