Good luck and let us know how it goes.
Generally I find the hen does well. It is the feed store chicks that seem confused. Have food and water (that they can't spill) in the nest box, with all the barriers up that you've got.
Place the chicks under her from the back end scooping the chick under her tail while you divert her attention with your other hand. Move slowly and calmly. Avoid lifting her. She can peck your hand if she must, but not the chick.
Usually the hen just looks at you with an "excuse me!" expression. Now the chicks, having been artificially hatched, are another story. They often don't know to stay under momma and don't head her calls for which they can get pecked. Stand by that night to make sure all is well. Usually they all settle pretty quickly that night.
The trick is light of day when the littles wake up and begin to panic at the big scary hen. You may have to keep an eye on them for several days to make sure the chicks have it figured out. I find my worst loss is the first day for chill and the second day for stranded with feed store chicks.
Good news (if you are in the Northern Hemisphere), we are entering summer so the weather is warmer and it takes longer for chicks to get chilled, so you have some leeway. (Cold weather is hard with fostering chicks because they can get very chilled quickly if they don't catch on quickly).
If momma stays calm and isn't flustered by her confused chicks, things should settle fairly quickly after a few false starts. Sometimes it works swimmingly. Other times, not so much.
LofMc
