Yulia - Welcome to TheChocolateLife!
You can produce chocolate from raw (unroasted) beans, roasted or unroasted nibs, or mass. Which one you choose depends on a number of factors. The further down the value chain you go (beans), the more work you have to do all around and the more challenges there are to making good chocolate consistently.
I can't advise you where to start, but there is nothing wrong with starting with mass (or nibs) - you just can't call yourself bean-to-bar. So that's a branding issue. With respect to cost, it's probably going to be less expensive working from cacao mass than from beans. However, you will have fewer options with respect to origins and roasting profiles. Balancing that, I have heard from people that there are issues with getting beans reliably into Russia - the brokerage situation can be difficult. You will have fewer issues with getting nibs or mass.
There will be a lot of bean suppliers at the upcoming salon du chocolat in Paris at the end of the month and at Chocoa in Amsterdam in February. They are not bean fairs, there are a lot of suppliers.
What I would suggest, if you decide to start with beans, is that you start with cheap beans (e.g., Ghana) as you learn the art and the craft. If you start with expensive beans (e.g., Porcelanas) you will be hesitant to "ruin" them and that will limit you in your exploration of what the beans have to offer. Also - there are lots of fabulous Trinitarios in the world (I just got back from a trip to the home of Trinitarios, Trinidad) - a lot more than Criollos - and I would start there before moving up to Criollos. You want to have experience making chocolate and making good chocolate consistently before you start with the most expensive beans there are.