I can tell you that paulownia is easy to grow and it can be coppiced and it grows quickly. I've heard it called "instant shade". I believe the flowers are useful to a number of insects. I can also tell you that the
wood is soft. I'm told that, being soft and easily worked, it's good for some sorts of woodworking, but I'm not at all familiar with that.
where I'm at, there are outfits catering to specialty woodworkers that could probably provide some information on
local demand and price, but I don't know what the situation is in Bulgaria (you're in Bulgaria, yes?).
personally, a plantation of paulownia doesn't sound terribly exciting to me. it's a nice
enough tree and useful, but not tasty enough to justify more than a couple of specimens. if, however, you're excited about the things paulownia is good for or you know folks who are, it might be just the tree to plant quite a few of.