One lone egg. . .and a housing dilemma

[2150MormonRd]

Yesterday my broody Wellsummer successfully hatched her first clutch of 11 out of 12 Icelandic eggs. (I have no rooster and bought her some eggs) Because of the way my coop is elevated, I thought better to bring her into a dog kennel in my dry basement for the last 5 days of sitting. She barely left the nest and did not eat or drink unless I put it in front of her. She is doing so now and has led the chicks to food and water. There was one lone egg left. She pushed it out from under her. I candled it and it looks normal and also did the float test and its viable. So without an incubator, I put it with a damp paper towel under the Brinsea brooder plate I have. I don't know what else to do with it but I'd like to give it a chance. Is there anything else I should do? How long to wait?
As for the others, I need advice. I plan to sell 8 but keep 3 and thought I should separate them from Mom and put them under the brooder plate. My dilemma is whether I should build a little separation area for Mom and the 3 babies I want to keep outside or just put her back and raise the babies under the brooder plate as I have other chicks before. It will be a long time before they can go out in the main yard because they can go right through the fencing but I want Mom to be outside asap.
I need some advice on what to do. Which would be the best way to raise them with the limitations I have.

Thanks

 

[Earthdale]

I would suggest keeping them with the broody, in my experience that has been the best and easiest way to raise chicks. As for the egg make sure to keep the humidity high around it.

 

[Tonyroo]

Keep the chicks with the hen. As for the lone egg, keep a moist towel around it not covered entirely and leave it under the plate. Hope for the best possible turn out.