Don't beat yourself up about it; this is how we all learn really. There's no substitute for experience, and no shortcuts to gaining that. The main thing is to observe, consider, maybe make some notes, and learn from any perceived mistakes so you don't do it again.
Not necessarily.
It sounds...
Yes it's tricky, and sometimes is not necessary - some hens can manage, some not, some co-brood happily, some don't. How far apart are the 3 hatch dates? 1 clutch has already hatched apparently; when are the other 2 due?