Eventually, the logo was finalized with this arrangement of elements and colors. The color of the side books and rings is taken from one of the colors of the interior of the store (a warm-gray), which I think nicely accents the primary logo color. I'll include a black and white version as well.
Overall, this was a great project to work on. The clients seem satisfied with the result, and I'm satisfied with the result. I'll keep my fingers crossed that response from people of Moscow is also positive. I guess if I see pitchforks and torches outside my window and posts on this blog drop off completely, we'll have the answer.
But it was still fun.