Hello Wojtek,I am from town located near Kaloferska Stara Planina-the mountain begins just at the north end of my town.I can help you with founding place to sleep-hotels and etc,parking-lot for car,reservations and etc.I know pathways in this part of mountain good too.
For this region-if starting point is Sopot-you can drive only to lift-station.
In Karlovo mountain begins just at the north end of the town and there you have to stop the car.
If you choose starting point Kalofer-you can drive to locality Panicite-but here you can find cheap transport to this locality-I will recommend you to leave car on the paid-parking in Karlovo or Sopot-it is more sure.
Send me some your coordinates-e-mail,ICQ-and we will talk more and will help you with everything,which I can.
My ICQ is 338-228-560
My e-mail top_2@abv.bg

Sorry for my broken english.