The short answer: No!
The long answer: We don't allow users to do multiple journeys at once. The reason for this is that habits are ingrained better when you focus totally on one habit at a time and make sure to complete it for a few days before moving on.
Overloading yourself with too many habits when you are feeling motivated can be counterproductive. You might be able to stick to the huge list for a while, but eventually, you'll get discouraged and stop all of them!
If you really want to take on more habits, you can add a custom habit to a routine, but please be conservative about this and only add one new habit at a time. Once you've done it for a few days and are comfortable with your ability to keep up with the new habit, then you can try adding another one.
What about a Journey and a Challenge at the same time? Please check this article.