Most people, probably myself included, should not tackle multiple languages at once. But that is not always practical, and sometimes we just can't be convinced otherwise. Here is my strategy on dealing with this.
Firstly, you have finite time. It may not be possible to do all that you want.
My own situation is that I have 4 languages 'on the boil': Latin, Greek, Gaelic, and Mongolian. Each of these has a different context, which shapes my approach. Latin and Greek I have studied a lot, but have little spoken opportunities. My need in these languages is more of an 'upkeep/slow progression' type. Mongolian is conditioned by having 3hrs of class, 5 days a week, and living in a country where it is the everyday language. Gaelic is a language I am passionate about, somewhat independent in learning, and aiming for more and more input.
One phenomenon I am seeking to avoid, and cultivate its converse, is that of having a space in the brain that is 'foreign language', where all L2s get dumped. That just leads to a lot of codeswitching problems. Instead, when working on a language, I want it to be its own discrete system, and I want to learn in that language and function in it as much as possible.
For this reason, I subdivide my day to transition from one language to another. I spend some time each morning with Greek and Latin, just reading and sometimes listening. Before Mongolian class I transition, by going over vocabulary, doing homework, etc. By the time I get to class I want spontaneous Mongolian bubbling in my head. When I come home from class, I try to transition to Gaelic, and actually expunge Mongolian from my active mental space. Again, some vocabulary, some reading, exercises, listening, etc., to work on that language.
This approach provides bigger segments of a day functioning or focusing on individual languages, rather than a more chop-and-change approach. It also tries to avoid moving from one language to another too 'quickly', but sets up more definite transition times.
All in all I am finding this more helpful than my previous approaches, which involved alternate days for some languages, or a little bit of everything in the morning.