How to open the gates on the Road to Rule

I believe the number is 5 Million. But here is the thing. Once you have that much the chest will be covered in gold and inaccessible.

To get rid of it all you have to give your money to the royal treasury which you can do if you are the king. If you aren't there yet keep playing.

If you're looking for a total count in one location, no, I don't think there is any way to see the total count that you have. They left out a total count for silver keys as well that's easy to access in the new menu.

You can view the map in the Sanctuary and hover over a location to see if you've received the golden key for each individual open location as it will show you either 0/0 if there's no key there, 0/1 if you haven't found the key, or 1/1 if you have found the golden key there. This only works for locations that you have opened through the quest so when you start out you'll only see just a few locations.