Are there any good heritage SC RIR breeders in South Dakota? I have been hatching chicks but I do not think they are dark enough as some of the pics I have seen in this thread.
20 wks they will be about as big as they will get. You could go a little longer if you wish but at that age they will be eating a lot of food and for what they will produce back in meat will not equal to the inputs.
For 5 chicks you should be able to just have a 75w light bulb in there for warmth. Also if they are fine with it being 75-84 degrees you should set it at 80 and then drop temp 5 degrees per week until they are at night time temps. If you are unsure of heat just watch them if its too cold they...
The spurs is right although some females will have spurs but you can tell by the beak too males are wider and more red. Also I've heard but never attempted that you can take a caliper at day olds and a leg over 2cm is male and under is female.
I would not take chances in spreading anything and keep her isolated until she is better. I would treat her with a respiratory med. Teramyicin would be easy to try. If she responds with the extra warmth she will come around within 36 hrs.
I would feed just a chick starter. It is better to have less protein in the cold than more. It is like doing a high protein diet to loose weight. In the winters here we feed a lower protein so the birds get more fat for energy to stay warm.
I would keep the humidity at 52% relative the whole time. I also would turn the auto turner on at day 2, 8 days for chickens is 1/3 of the development process. What kind of incubator are you running?