How to observe invoice creation / custom sales order status?

To answer such questions, it is enough to have generic Magento 2 knowlegde ans skills, and is not needed to change anything in the Stripe extension, and even is not needed to read its source code.
So the question in not related ti the Stripe extension, and, as I said before, I can answer such questions only on the terms of my generic Magento 2 support service.