Ok, I think this has potential but I wanna vent out my grievances.
It is clear that the mangaka is a history buff. He doesn't just slap some Wikipedia entries in the speech of his MC, some real thinking is happening. I mainly think that from the Machiavelli thing (which I still don't think was good criticism of Mach's work, but it is criticism), normally author just quote him without critical thought. Probably most figured it out, but clearly Lemuria is just Byzantium, this is most likely the age of the Palaiologos restoration.
I find the stuff with the little girl a bit creepy, but I think it's apparent that, while he has the memories of a 40 year old salaryman, he doesn't have the personality of one. He's not the salaryman, he only has his memories and knowledge, as it appears from his more childish outbursts.
So, the plot is mainly in good hands, BUT
It shows some of the BS mangas of the genre have. It's mainly 2, really: usage of technology there's no way people of the period would know about (and gimmick-ification of the economy), and the FUCKING TOURISM.
Of the first kind, this manga seems to show more restraint (though it has only been 4 chapters). The technology the little kid has brought are mainly within the technical competence of the age. I don't like the idea that he saved the economy by bringing in coffee, usually single plants don't evolve the economy like this, coffee was around for like 300 years (when it started being produced in reliable quantities in colonial plantation) before coffee shop became the gathering place of the educated. I know that he also put some admin reforms in place, but coffee is ostensibly a gimmick.
Now, the latter is what REALLY grinds my gears. I used to be able to ignore it, but goddamn it seems like it stuck. TOURISM IS NEW. YOU CAN'T USE IT TO REVITALIZE THE ECONOMY. Travelling, back in the day, SUCKED. It was dangerous, you could get lost, it took too damn long, not to mention getting robbed or killed or getting ill and dying. In Europe, people started travelling for leisure in the 1700's. Even then, it was the luxury of barely, like 5%? That's a generous estimate. Before then people travelled, yes, but only for necessity: pilgrims, merchants, scholars... to construct infrastructure for an industry that cannot exist before a long long time is foolish. To be honest, if he wanted to attract "tourists", a particularly grand church, preferably with a lot of relics in it, would have done a better job than a goddamn museum. Better yet, roads and patrols to protect commerce.
With that said, the manga doesn't overindulge in this nonsense. The two other buildings he showed off were reasonable. Though what the fuck is up with slavery, does that shit exist here? Did they mistranslate "serfs"?
Overall, if you like the genre don't miss out on this one.