Is it okay to exercise every day?

Hi r/fitness :-)

I've been running for 3 weeks on Mondays/Wednesdays/Fridays, and doing bodyweight workouts (courtesy of r/bodyweightfitness) for about a month and a half every Tuesday/Thursday/Saturday. That leaves Sunday as a rest day.

Here's my problem: soon I'll start training for a marathon with a plan that involves running 4 times a week. I heard it's best not to do strength training and running in the same day, so I'd be working out on the 3 days I don't run, which would leave me with no rest days. Is that okay? I Remember reading somewhere that my brain actually needs me to have a rest day, but I'm not sure if that was bro science or not. I also plan on starting Krav Maga but I'm not sure if it would be okay (health-wise) to do all of that together.

td;dr - how should I organize myself (in a way that's not detrimental to my health and/or results) with a 4 days/week marathon training run, 3 days/week bodyweight strength training, and if possible 2 days/week 1-hour Krav Maga lessons?