The main road paralel to my route was indeed strongly disadvised by local cyclists to being very dangerous. A shame since this meant that I had to refuse an invitation by 3 monks to visit their (very scenic) monastry which is only accessible via the main road. It does help though to speak basic Russian as that makes retrieving info from locals a lot easier.That's very interesting. Although you hit Russia quite close to where I did, that's a very different route to Moscow than the one I planned. What sort of roads were you on and what sort of bike/tyres? I (thought I) did tons of research and found only one possible route for my normal touring bike tyres and it wasn't anything like your route.
The last bit towards Moscow I planned on the fly, using locally sourced streetmaps.
I used a combination of online maps (Open Street Map) and locally sourced maps. The only dodgy roads were near lake Selinger, about 80km of gravel. For the rest asfalt.
I was using 37mm Vittoria Randonneur tyres.
I can advise to use the old audax routes of Baltic Start St. Petersburg as a template for your routes.