Re: Any point in doing CF only 3 times a week, as part of a "fight fitness" regimen?
I've been seeing progress doing CF only twice a week; you should certainly see benefits from 3x per week.
Four days of serious martial arts training a week is a lot, even without the CF. When I trained that hard, I started to accumulate aches and pains that just didn't have time to heal. YMMV, but in your position I would definitely be alert for signs of overtraining.
How to get more rest? That depends on your goals. If CF is more important than martial arts, dump some of the martial arts training. If martial arts are more important, dump one of the CF classes. Or keep both on the schedule but take extra rest whenever your body tells you it needs it. Whatever you do, be sure to eat enough and get enough sleep.