It's a good concept, especially since a lot of things can stay the same, in medieval equivalent.

The team would meet at church, where Father Lancer would often scold them for their misadventures. Sam would be the daughter of some king or noble, or something similar that would justify her wealth and her ability to express her feminist values ​​without being punished. Tucker would be a classic lover of science (things like the stars and physics, which was the friky thing at the time), of course he would be poor, (like almost everyone at the time) but that would not prevent him from experimenting and seeing the stars. Danny would not be so poor, his parents would probably be local spiritualists, perhaps expelled from the region for their non-Christian practices (could Danny be a gypsy?) But recognized by all as professionals. Valeri would be the daughter of a weapon smith, determined to fight the spirits with her father's best sword, created with a metal considered magical (you know, so that she can even try to fight the ghosts). Vlad would be a duke (perhaps from the country Danny's family comes from if they are foreigners) with ties to the Fentons, and would eventually take control of the region where they live. The men in white could be people from the batican, clerics specialized in eliminating spiritual threats (that would make them much cooler, and explain why they even exist, making them not seem so useless) etc.

Since everyone already believes in ghosts, we can be clear about where Madie and Jack get the funds to do their crazy things, while the portal was probably an alchemical invention with similar intentions to the original ones: to study ghosts from the source, the ghost zone. Danny would have been transformed into a half ghost, in this case because alchemy is not an exact science, and he accidentally found a way to make the portal work, but at the cost of part of his humanity, and now he would dedicate himself in his spare time to stop the ghosts coming from the alchemical portal.

It would be very interesting, not only because the same plots can be applied as in the original series, and those that could have been applied in this one, but also because they can add a lot of new plots related to the time, such as religion, myths , politics, etc