This mod has A LOT of potential and I think it is theoretically even more in-depth than 1257 AD, especially with your additions of Finland and its correspondent tribes etc.
I also love that you have made individual units for each nation with their own names, you didn't see that in 1257 where like all of Europe had literally the same units. You have nationalized the units, and that is something I really love.
But there are some issues. For instance when in battle, fighting as a freelancer under a general, all both sides did during the battle was to move right all the time. No one ever moved forward, only to the right, walking in circles. There are some battle deployment and AI improvement mods you maybe might be allowed to implement, that would make this amazing
Also there are some graphical issues on the world-map, like "square-ish" rivers, but I think that is an easy fix later on.
And some small things, the Baltic tribes seem a bit to heavily armed. I mean, their armor is often a bit too advanced regarding the fact that they were actually fighters who preferred to fight with light skirmishing troops, specializing in javelins. Whenever I visit them it feels like I am seeing a noble prince of Novgorod, and not a pagan chieftain. Also, their banners are slightly too unrelated to their culture. You should see to replace them with more Romuvian (Baltic pagan) motives