I think the best way to go is to learn one language first and apply the 80/20 rule to it. Once you have enough efficiency on your first language, learn the next one applying the 80/20 rule once again and then learn another one until you get to five languages or more. Then once you have the basics down on the languages you've learned, you can relearn them and study them to a higher mastery level. In my experience, I found that it my Spanish helps in my current learning of French because they have a lot of similar words or roots!