Why would you kill the embryo? You can tell if it's fertile or not by candling.
https://www.youtube.com/playlist?list=PL8AKDZ9NpcmHv6Q2j0K5q07yrPT5nOgMV
Yes, early or late hatchers are more likely to have problems. That doesn't mean that you won't get perfectly healthy chicks if they hatch early or late, but the chances of problems is higher.
With enough space, 3:5 may work out, but be sure to watch them just in case. Some eggs will probably be infertile, but it may not be consistently a single hen. You'll know after they've been in the incubator for a few days.
17 is normal. If they hatch before then (day 15 in your example) the temperature is probably a bit high. If they hatch after that (up to day 21), your temperature is probably low.
Never trust the readings on your incubator. Always have a calibrated thermometer or three in there.
The males won't necessarily mate with just one female (so your thought about having females with always infertile eggs isn't quite right), but for harmony's sake, they do best with an equal number of males and females. If the ratio is off, you may get a jealous bird or two who may squabble and...
Button quail do best in pairs, but with that much space the odd one out won't be a problem. It's coturnix quail that need about 5 females to 1 male. Buttons are not as aggressive as coturnix.
The ideal ratio of males to females is 1:5. The standard hatch rate is 50% of each gender. That means that if you plan to hatch them, you need to have a plan for the extra males.
They can be quite tasty.
https://www.youtube.com/playlist?list=PL8AKDZ9NpcmGRSF-6vcvoL3OP2K-laGvu
:welcome
Since you're new to new to quail, I would recommend that you check out the articles in the learning center. The link is below:
https://www.backyardchickens.com/articles/category/quail.32/
@007Sean has a lot of experience with bobwhites. I've tagged him here so he should be along to answer.
Personally, I would remove all of the birds, clean and rearrange their pen, then put all of the birds you want together in at night so they're together when they wake up in the morning.
It sounds like it was a bit premature, but they do sometimes hatch before completely absorbing their yolk. As long as they're not bleeding, they usually absorb it and are okay.
It can take up to 24 hours from pip to zip. If it doesn't zip in that time, there is most likely something wrong. You may choose to assist, but if you do, be aware that chicks that have trouble hatching usually have trouble because there is something wrong with them.
Here are a couple...
I actually do know that. Chickens are pretty domesticated, which makes them easier to train and they do learn fairly quickly as long as you treat them like chickens.
Quail are quail, and you have to expect them to act like quail. For their tiny size and prey status, they act as expected.
I went out to coop the chickens and found that they had cooped themselves and all I needed to do was shut the door. Chickens really are smarter than quail. Not that that takes much. Quail are dumb as rocks.
If they're eating chicken layer feed, they're definitely suffering from malnutrition, but the twisted neck has me worried. I strongly recommend getting one of the bodies tested. The twisted neck could be a sign of Virulent Newcastle's disease which is highly contagious and frequently lethal...
That looks necrotic to me. I'm guessing injury, quite likely something like you described. You're doing the right things, but don't be surprised if the black part dries up and falls off. Your bird will be okay without the toe.
I use cardboard boxes turned over and cut two holes in them. They also love the dollar store baskets. They feel hidden but can still see out of them. Again, cut two holes so they don't get trapped in case a bully chases them into one.