Originally Posted by
fallinasleep
Is this based on personal experience with buying Trans-xxx tickets in Russia?
While I agree that one is better off buying the ticket in Russia, your other advice about making stops wherever the OP sees fit is not exactly good advice unless things have changed since I took the train in 1998. Back then, the fare went up immensely due to taxes on domestic tickets.
What I would do is start in St Pb then take the overnight train to Moscow. I would then recommend two stops, at Irkutsk and at Ulan Bator. If necessary, buy only a Moscow to Ulan Bator ticket since the OP could easily spend a month traveling around Mongolia...then it's just a day's train ride to Beijing.
Yes - it's based on personal experience. I'd hesitate to say it's about Trans-xxx tickets though - simply train tickets on the routes that the Trans-xxx trains follow.
It really is impossible to gibe more advice until the OP comes back with better ideas regarding timescales.