the exchange rate used in the manga is fairly accurate to the historical rate (though with some minor change for dramatic effect) and the story while fictional is built around these historical point in time. So yea it's historical
The original doujin is still on-going (chapter 9 has just been released last month) chapter 7 mark the current latest tankobon release (which is just several doujin releases stiched together with extra info) by kadogawa and the end of the 2nd volume. So if the scanlator want to wait for the 3rd...