Don't take developing eggs out of incubation to kill them, that's not nice at all. If you want to do 1 at a time then try incubating one at a time and checking them on day 3. I really don't like the thought of raising 1 at a time.
Solid article with good information, I disagree with a few points (eg. Adults can have 14% protein chicken feed with no issues and fertility ratios should be higher than 2-4, 2-4 is risky due to quails habit to overbreed. 5-6 is best for fertile eggs).
I love the repurposed trampoline frame, however it doesn't seem very wind nor predator resistant. I don't see much information on the coop itself unfortunately.
It's a nice looking coop, I do feel that ramp is quite steep and it doesn't look big enough for many chickens. I can see you have ventilation that you have to manually open, some constant ventilation would be great. Any photos of the inside?