If you plant too early the emerging shoots will get frosted so be prepared to earth up at any hint of frost.
Let the long shoots toughen up before you plant them - they are very fragile and if you break them all off you won't get a crop. When you plant them, pull the soil around them carefully so they don't break.
The shorter sprouts on the 1st earlies are fine - chitting them is just to give them a head start before they go out, or to prevent long pale sprouts forming as with the ones you kept in the box, but it's not essential.