Definitely look them over for cracks... "look" at them with your fingertips to feel any chips. Coturnix are hard to candle, so your best bet is to look them over carefully. Let them come up to room temp for 4-6 hours before putting them in the incubator.
Because they have a 16 day incubation period, they develop rather quickly. If you can candle one (use a very strong penlight on the big end of the egg) before you incubate, you will notice that the light shines throughout the egg, illuminating it. By day 4-5 you'll start to see a reddish tint. I don't think I've ever been able to see an actual embryo in there, but by day 7-10 your egg should be fairly dark, with only the airsac showing clear. If, at day 10, your egg still illuminates completely when candled, it isn't going to hatch.
Generally, I put them in the hatcher and bump up the humidity to 75% on day 14, say a Hail Mary! and wait to see what happens.
Usually late day 16 you'll find a little pip. Then a few hours later, more pips. Then, as if by silent gunshot, they'll ALL start zipping at once, racing eachother out.
It's so much fun to watch.
Good luck!