Well... The Russians didn't really do any fighting in Kosovo. They just squatted on an airport for a while. And as for Afghanistan, are you kidding? The youngest of those Russian soldiers would be in their mid forties now. If there are any experienced Russian troops lined up on the Ukrainian border they got their experience fighting in Chechnya, Dagestan, Ingushetia, Ossetia, and Georgia. Most of the fighting in those places amounted to homicidal policing, not combat. Pity the Ukrainian civilians if they do invade and the Ukrainian army can't repel them.
If the Ukrainians do fight, I'd pity the Russian troops. Chechnya plus its Caucasian cousins came to a few million people in postage stamp-sized areas. Ukraine is the size of Texas with 50m people. Armed with captured WWII weaponry, Bandera and his men killed 30K Russians and collaborators in a period of 10 years. Nobody knows how things will play out, but a rerun of the partition of Yugoslavia will see, at minimum, tens of thousands of Russians going home in body bags.