Been there, done that
Last year I spent 3 weeks riding a BMW F650GS thru Slovenia, Croatia, Serbia, Bulgaria, Macedonia, Albania, Kosovo, Montenegro & Bosnia. I was solo - awesome adventure, no problems.
I used Adriatic MotoTours in Slovenia. I rented the bike from them. They booked the lodging, provided maps & GPS navigator. Check out their website - they are Eastern Europe experts.
Send me a PM if you have any questions.