I like the fact you touched Siberian cultures (Am working on a mod that does Siberia as well as Tibet), but there are a few mistakes:

1 - "Evenk" and "Tungus" are really the same ethnic group, the Evenks. If you want to maintain the split, I would rename "Tungus" to Evenk, and "Evenk" to Solon.
2 - Selkup definetly deserves a culture. I would put it between Khanty and Yeniseian and place them in the ugric group.
3 - Yakuts did not inhabit that much of Sakha by 1400s. Some sources say they werent even in Sakha by that point, but even if they were, I would only put them in like 2-4 provinces including Yakutsk.

Oh interesting

Sorry I don't know if I resolved this or even saw this, I will be sure to look into it soon

I know I should add Selkup and will do such later along with some other planned things

Sorry for the delays
I know that Tungus Evenk are technically the same, traditionally Evenki were called Tungus, the devs clearly just divided them on the Solon Evenki line with Evenki having the traditional name in Russian and Solon keeping Evenki, I will leave this alone for now, but may change it later

I have however changed around the Yakut (and Dolgan province which I also made Yakut) and a few of the Buryat provinces which will only change to other cultures near the end of the game.
So consider 3 resolved, unless you have more suggestions.

2 will be resolved when I add new cultures, which is in a coming update of mine planned.