How do I fix and grow Japan’s economy

The Japan I took control over from ashikaga had abysmal control and wealth to tax base ratio of 5:1 and my economy is at a negative. How do I actually invest my saved up 45k ducats efficiently to fix this? Should I build roads or invest in a navy to improve maritime presence and focus on harbor access for control instead? Sadly I failed to push naval enough while being a BBC so no +1 naval governor reform as well.