In many ways Russian fascism would be somewhere in the middle between Italian fascism (which I think of as 'fascism proper') and Nazism. It would probably be defined by the following features:
- A rejection of the 'overly material' and 'decadent' culture of the West, which would be oriented more against Anglo-Saxon and French liberalism than Central European or Mediterranean culture.
- A deep distrust of Catholicism and the Pope as a subversive element (likely with some nasty consequences for Poland).
- Favoritism towards Orthodox Slavs, with some internal conflict between the more strongly Slavic elements and the Hellenophile (and pro-Armenian) clergy.
- Conflict between 'secular' and clerico-fascists.
- The reduction of Muslims to de jure second-class citizens as opposed to merely de-facto. Whilst not looked down upon to the same degree as atheists perhaps, there may well be justification of Russian rule over Muslims as a 'crusade' against the 'heathen Tatars'.
- A powerful drive to seize Constantinople as 'Tsargrad' which will lead to conflict with the British and French over Turkey and Greece.
- The Russofascists are going to absolutely love the Iron Guard in Romania. Not only that, but they'll support Bulgarian fascists and Royal Yugoslavia. Although they aren't really fascists, per se, Zveno in Bulgaria is likely to be supported by Russia, as they sought to suppress VMRO, an organisation which had the potential to flare up the Macedonian question and create a split between Bulgaria and Serbia, which would make Russia's dominance of a Balkan Orthodox bloc very difficult. They will also support Metaxas in Greece. It's important to note that in most of these cases they won't align 100% in terms of ideology with these groups, but are close enough in being conservative, Orthodox and essentially anti-liberal, anti-individual and anti-materialist.
Interesting idea. The whole far-right trope of "dictatorship is a native institution, liberalism is a foreign trojan horse" did already exist in some reactionary circles (ignoring how the Imperial autocracy owes at least as much to Peter the Great's Westernization as to old Muscovite institutions, but hey). Working out the economic side of the ideology is going to be pretty hard, though.
The Poles probably get away after WWI, by being upgraded to an independent state or at least an autonomous puppet.
The wholesale repression of Tatars also doesn't seem that likely. The Tsarist far right did not view this community as much of a threat or target, and often found itself allied with Muslim landowners and other conservatives. For example, the Black Hundreds even had Muslim branches in Tatar areas. They generally hoped for the Empire's diverse subjects to unite (and then, of course, gang up on the Jews and leftists).
So I imagine this hypothetical regime will make Jews the major target of repression; maybe together with local Germans, Georgians, Finns or Lithuanians.
There's also the impact that having ~fascism instead of communism in Russia will make on far-right movements in eastern Europe. The Iron Guard might still get somewhere, but Metaxas, whose rise was 100% artificial, will get nowhere at all. In general, they will all need to do some rebranding.