Russkies, help me to prepare my itinerary

Vladivostok to Moscow or Beijing to Moscow Transiberian Rail was in my bucket list for long.

I have valid Japan visa, I can fly in from Riyadh to Japan and do Vladivostok to Moscow or fly to Moscow and do Moscow to Vladivostok.

I may avoid Beijing, due to my Taiwan residency earlier and visa to China.

May I ask, what is my best approach on this itinerary from Riyadh?