I do not know anything about Montana or Pleven region but am very familar with Stara Zagora region. I have 6 houses there, soon to be eight and am moving there later this year. I work for a small agency there (see signature below) and so can help with property purchases, renovations, inspection trips etc.
I personally love the area around Stara Zagora because you have the Balkan mountains, you have lakes, hills, forests...there is a golf course planned, spa resorts, Thracian tombs etc and as in the centre of Bulgaria, most places very accessible.
There are a few of us Brits in the area. I know of one or two living there permanently and certainly there are many with holiday homes.
I have a great Solicitor in Stara zagora I can recommend highly.
Not sure exactly what your concerns are about the power of attorney. It is a regular practice to give your agent, lawyer etc power to sign documents on your behalf to complete house purchases etc, register properties with utility agencies and so on. My Bulgarian business partner has power of attorney to buy property for me, my lawyer has power of attorney in relation to certain company aspects, my accountant has power of attorney for taxation things.....
Thanks,
jain