you have done great, they look excellent in the pictures.
and the fact that its your first hatch, several people dont get any on a first hatch with chickens, ducks are a little harder.
now that you have seen how it goes once, next time you can go at it more relaxed. im not saying embryos are hard to kill, but they are more durable than most people want to think.
most first time hatchers want to assist way to early, you listened to sumi and didnt get into a hurry. you assisted the hatch flawlessly for the most part. the one you culled could have potentially been saved, but it could have had issues too; and that's a decision we have to make as hatchers.
i think everything is fine with these ducklings, of course i cant hold them or see them directly - so just use your best judgement.