How many languages can I learn at the same time?

The answer to this is simple.  You can learn as many languages as you like at the same time. 

However, when you first start to learn a language, it requires a lot of effort.   It is well known that starting a new language, especially your first, is the hardest stage to work through.  Therefore, in the early stages of learning a language, I would recommend to only focus on one language at that level at any one time.

However, once this challenging stage is over and you reach the intermediate stage in your first language, you can then pick up your next language whilst continuing with your first.  Providing you have the time and energy, you can then easily work on two or more languages at the same time. 

Learning languages has to be one of the most rewarding processes ever.  All it takes is a regular time commitment with each language, ideally every day.   This is the only secret to your fluency dreams in many foreign languages.