Do not quite understand of which region you want information about.
No problems to get food, fuel and accomodation between Chita and Chabarovsk, the far east is very developed anyway.
As to Mongolia: I stayed more or less in the Ulan Bataar region and the tracks were not as bad as I thought they would be. Also, I saw pictures of western Mongolia which suggest that, as always, you'll have the choice whether to ride the main, relatively good tracks (rivercrossings might be challangeing though) or the minor, difficult ones.
I did not experience difficulties of getting food and fuel, but of course we did plan my trips a bit more closely than we would have done in other countries with a better infrastructure.
Also, it would not hurt to carry food and water for one or two days.