Per CNN and the BBC, he has forces all the way up to Lipetsk already. In what quantity, we don't know. Prigozhin himself is parked in Rostov, as far as we know.
The just-announced travel restrictions in Kaluga bordering Bryansk and Smolensk are interesting. That would be consistent with dumping a bunch of bridges into the Oba, as a delaying strategy. I don't think Wagner has assets over there. It could also be that's the direction from which Putin is planning to scramble some assets. It would be consistent with losing Belarus to save Moscow, but I don't know just how much he had in that direction.