Hi Arber and welcome on here !
That's a long bus/train ride you have planned.
The best but maybe not the cheapest solution I've came up with is taking a flight from Pristina to Budapest (around 300 euros - click here
for infos), then a train to Lviv (don't know how much it costs, more infos here
There are trains coming in in Lviv from Krakow and Warsaw.
Hope this help. Good luck with the planning !