@koneko: Well, I didn't start Russian until my Korean was at an intermediate level. It is hard to split my time between the two, but I enjoy it in the end. I think it depends on how fast you want to progress though. If you want to progress in one language as fast as possible, then it's probably better to pick one and focus on it. If you're not too worried about progressing super quickly, then two is okay. Also, Russian is a hard language, but Korean is still considered more difficult than Russian for native English speakers, so I think the difficulty of the languages you're learning is also important to consider. Japanese and Korean do have similar grammar though, so your knowledge of Japanese may come in handy there.