i agree, the risk of direct conflict is limited.
That being said, if Russia were going to fight a conventional war with NATO - this would be as good as it gets for them. This is their backyard and the logistics train would be much shorter for them, than us.
Putin does have some leverage here and could easily enough move some airborne troops into Serbia. I doubt he has the gumption to try to insert them directly into Pristina, although Yeltsin pulled that off back at the end of the Kosovo bombing campaign.
I agree. It would be their best shot at inflicting some damage before they inevitably had their asses handed to them.
The problem for Russia is that if their planes entered Kosovo airspace, NATO could obliterate them pretty handily - so Russia's best bet is to try and get as many Russian troops into Serbia as they could before Romania's government formally requested NATO aid for the violation of their airspace.
So Russia could deploy a bunch of their troops on the Serbia-Kosovo border, as you say.
If they invaded Kosovo at that point, NATO would make short work of them - and Russia would have real difficulty extracting their troops from Serbia after the failure of their little adventure.
What Russia sees here is a confluence of political and economic ($100 oil) events that can help them gain leverage with the EU.
Putin isn't stupid enough to initiate a war that would expose how weak Russia's military really is without gaining him any material advantage.