Exactly. Once the pulse is under way, you can (and should) eat protein and carbs to capitalize on that fat pulse.
GH is powerfully anticatabolic, so yeah I would think it would help preserve muscle on a potentially catabolic fat burner.
Is it fat free cottage cheese? (do they make ff cottage cheese?) If so, no problem. If it ain't, the fat should interfere with the GH pulse initiation to a degree, but not as much as carbs of any sort.
Sure 20 minutes is fine. Even 15 is fine, just not less than 15 to be safe. The Ipamorelin hits immediately. The somatotrophs will be doing their thing probably within 10 minutes, but 15 is just a safe waiting period.
If you want to go 3x daily, I'd do it every day, unless it's a cost issue. You're recovering even on cardio only days, right? Keep that pulsation big on those days too.
As for for question a while back on preloading a pin, sure. I do that. Iapmorelin is not nearly as delicate as synthetic GH. You can even drop it and it won't damage the amino string. If your gym is like stifling hot though, might not be a good idea to carry it along with you.