mmmm, lots of questions.........are you coming to bulgaria to live permanently, which means giving up residency in the uk. many people choose not to give up uk residency.
long term residency is granted after 5 years in bulgaria. a litchna karta card is your means of residency which has your identification number.it lasts as long as your passport/ethic card does and then needs to be renewed.
I dont know if your coming to work or retire, are you of pension age as you will be entitled to bulgarian health care but not uk health care.
need to know what your plans are really and are you ready to give up uk residency. or are you sharing your time between the two countries.