What if I have serious diarrhea during my 7 day break? Considering I won’t be taking any pill during that time, would that put me in the pregnancy danger zone?

No because break pills don’t contain any hormones & as you said you’re not taking any pills.

Won’t the diarrhea compromise my protection from the 3 weeks of active pills? Lower the hormones from my body or something along those lines?

No it doesn’t.

Not unless it's within 24 hours of starting your new pack