The 9cm x 15cm is print size. I'd suggest working larger, as when you scale things down - it makes everything cleaner looking. Think in scale, I'm probably going to work 9 inches by 15 inches, because I know my computer can handle it. That may not work for you.
I'm fine with not using Russian, I'm rather fond of the bird idea. However, I think you could have said something earlier, Curly. But, thank you for speaking up now.
While we don't have the same drawing style, we still need our work to be unified. So, having some of our 'characters' wearing Russian clothing, and Curly's not - would separate our work entirely.