It is often unclear if a certain hut has a warden at a certain time. Unserviced huts, which are easily accessible e.g. without special equipment such as those close to ski resorts (Banderitsa Hut) are often locked. Unserviced alpine huts almost always are unlocked and have a room with many beds, blankets, and a wood stove, with plenty of wood. Good practice is to leave the facilities more orderly than found, and slip some money under the reception door.
Due to the uncertainty and difficulty of a rescue, a conservative approach to these mountains is advised.
Wolves have cohabitated Bulgaria with humans since the beginning of our time. Wolves fear and avoid humans. Likewise, humans fear and avoid wolves. Mind your manners, and you may have a problem with a dog, but not a wolf.
I may have seen one wolf, which was interested in a dog, which was following me and had a limp. The wolf was not interested in me.
I saw a few chamois. Otherwise, I saw many tracks of boar, deer, wolves, but no bear tracks.
Maps of slope angle classes can be inaccurate, maybe due to the lack of ground truth but are sufficient. I used Gaia GPS, but would not use it here again. CalTopo has better slope class angles in the Pirin and Rila Mountains as of writing this in late 2022.
Iskar Tour maps are the best printed option. However, they are very delicate for use en route, and require forethought how to stow and access them practically. They can be difficult to obtain outside of Bulgaria.
The website bgmountains.org has routinely updated map tiles for offline use with a mapping app such as OruxMaps. These are the most detailed electronic maps for navigating routes in Bulgaria. The download is free, a donation is cool. They also offer a map tiling service:
The best combination for mapping data, as of writing this in late 2022, would be to add this tiling service to your CalTopo layers and combine that with CalTopo's most accurate slope angle class.