Search this forum for Bulgarian topics; you will find much of the information you need.
In general though, if you bought a property in the recent wave of developments in either the Black Sea resorts or in the ski areas, you are siting on huge losses and the rental prospects are bleak. If you haven't already furnished the place, it might be worth stalling on that; don't throw good money after bad. In particular, don't fall for the "furniture package" deals offered by rental agencies; the old story that you need an expensive fit-out to attract good clients is essentially a scam.
If you like the area where the property is situated, and you intend to spend a lot of time there, then go ahead and furnish the place, but do it yourself in the same way you would at home -- go to furniture shops and buy the stuff, there's no mystery about buying a bit of furniture. Unless you intend to use the place though, lock it and leave it, and put it down to experience