I'm still in the phase of shoring up my German to make sure it's at a strong C quality. Simultaneously, I'm trying to start the long process of bringing my French up to a B. In order to do that, though, I need to pass the C2 DALF so I can start my master's next year in Paris. My focus on French has had very noticeable effects on my German, Dutch and Swedish. A coffee chat with a Swedish friend of mine today involved a lot more blank stares than usual and when I tried to catch up on the German elections between classes today, videos that would have been simple to understand before suddenly took a lot more concentration. I think my move back to the United States from Austria is partially to blame, just due to the fact that my access to materials is different (not necessarily limited, but different). So, I was wondering if anyone had suggestions for some daily routines or regular practices that make maintaining multiple languages easier? Or perhaps in my stage of the game (perfecting two and adding one) is it better to just focus all my attention on one at a time?
I would focus on what you think will be paying your bills in the near future. So FR-EN in both directions or FR DE SV into EN. You're unlikely to consistently do both early on.
If you're set up to be in France for an MA then it looks like the former is already a bigger part of your plan.
If you want to do FR DE SV into EN then you should be listening to radio, podcasts, watching parliamentary debates etc in all three languages each day because that is what your work will be like - a SV speaker will follow a DE speaker and you'll have to interpret both. You can't get out of practice in listening to one or the other! I find podcasts extremely helpful because I can listen to them on public transport or wherever. If you do that consistently you quickly find yourself listening to a couple of hours of useful material each week.
From what you say it might be that your SV or DE are still too weak... but dealing with that is another question that's been answered here elsewhere already.