Few things in here. A box will only serve you for very little time if you bring Echo inside the house with her chicks. Reason being is because after the first 2-3 days, she probably will scratch around teaching the little ones and accidentally spill or tip over your water container (which by the way has to be shallow, just in case the little ones get in, they don't drown. I used in the past a big dog kennel and it was much more manageable because is plastic and also they may have more space, but even if you have a big wide bucket, it may work.
Advantages of having the broody hen inside: She will take care of the warming the little ones to the right temperature. She will teach them to eat, drink and all other birdie things they need to learn + you get to enjoy one of the most beautiful scenes there is to see.
Disadvantages of having the broody hen inside: Space mostly. The broody needs to have space to stretch and move around, not huge amounts of space, but enough that she can walk, stretch and flap her wings.
That said:
So there are two things you can do.
1. If all the eggs are due to hatch at the same time. You can take all the little ones and place them together with Echo (under her) as soon as they hatch and are dry, the sooner the better (place them under her from behind the tail and preferably at night. You do not want her to realize you are inserting baby chicks. Some hens don't care (I heard sikies, are great at taking anything you give them, but I personally don't have any silkie, so could not attest to the truth of it), but some hens will reject them within hours of adding them. I had one of those. The problem is that if you get a great hatch you will end up with more chicks than she can cover. I suppose if she is inside and you place a towel on partial part of the box, to keep the heat, it may work.
2. You can take all the little ones without Echo and bring them inside and place them under a heating lamp.
In either scenario, you cannot bring the chicks outside until they are fully feathered (around 6-8 weeks) and it has to be controlled. Their little bodies cannot produce enough heat to sustain them against the outside temperature and the wind and their feathers cannot hold enough heat at that age. So you will end up with chicks inside the house for a much longer period that you may want to. Other people do it differently, but I personally have never brought a baby chick outside without a period of acclimation. At first I wait for a sunny day (not windy) with temperature around 65-70 and let them out on a cover section of wires for a couple of hours (watching them quite often). Then slowly as the weather stays warmer you can leave them in a protected area run (no rain, no snow, as little wind as possible) for a day and then another day and bring them inside at night. Eventually they will have gotten adjusted to the weather and can stay outside at night inside a coop with not too much drafts of air. For example the ones I will be hatching now, will not see the outdoors until probably April depending on how the weather cooperates. Never put the little ones and the mother with the rest of the flock, it will be disaster. Also keep in mind any predators you may have lurking around. Little chicks are easy prey, a lot easier than the adults. Hope my sharing of what has worked for me helps you make good decisions of your own.