>>9 In my experience, it is better to start learning other languages after you've reached the upper-end of B2 in whatever language you're learning. Focus on one until then. That way, you're not overwhelming your brain with so much new information. Also, never start two at the same time. Your brain needs time to recover and process all the stuff you're learning. Which takes time. It may not seem like you're progressing right now but as long as you're consistent and continue doing meaningful activity in the language, you will progress.
In my experience, it is better to start learning other languages after you've reached the upper-end of B2 in whatever language you're learning. Focus on one until then. That way, you're not overwhelming your brain with so much new information. Also, never start two at the same time. Your brain needs time to recover and process all the stuff you're learning. Which takes time. It may not seem like you're progressing right now but as long as you're consistent and continue doing meaningful activity in the language, you will progress.