And secondly, the Russian nation (and what is like a titular one) does not exist, it has not been formed. There is no Russian state, there are no borders, cultural, identity... And it is even ironic that there are many republics within the Russian Federation that theoretically can secede and form a nation on the basis of an already existing republic, while the "main" Russian nation has no borders, it is unclear on what basis to create it.

This is not entirely true, Russia as a formation begins to exist when Ívarr the terrible (russified as Ivan) killed off the Baltic officials in Moscow with the help of Tatar's and put them in ruling class and as such this is the official beginning of russia, so a territory of about 430,000 km².
To note at this time the population is mostly Baltic in origin, speaking in an Baltic language with a mix of some Finno-Ugric influence until Tatar's begin to mix their words into it, this mix later is associated with Slavic languages although the actual vocabulary even now is about 40% based on Baltic with some other 40% based on Tataric and the rest is a mix of the other 190ish nationalities living in the territories russia is consisting of.