I can recommend https://www.seat61.com/ https://www.seat61.com/ for information about longer-distance train travel: frequently updated, lots of useful informati

I can recommend https://www.seat61.com/ https://www.seat61.com/ for information about longer-distance train travel: frequently updated, lots of useful information, discussion of different route options, etc -- he has a page about Trans-Siberian railway journeys.