I'm not sure I'd try learning more than two at the same time, but I find it helps if the languages you're learning are very, very different. In my case, I'm learning Cantonese and German at the same time. This is fine, since the languages are so different that I never confuse the two.

I would not suggest doing something like learning Spanish and Italian at the same time, since the languages are very similar. In that case, I'd wait until I was very comfortable with one before starting the other. :)

I want to know as well~