Rhea Chicks are so much fun! It depends on the age of your chick on how difficult they will be in my experience. The larger chicks, I definitely recommend casting artificial legs...the very young chicks you can just use leg injection fluid and they are fine. The leg shrinkage is nowhere near as bad on Rhea chicks as it is on Ostrich chicks in my experience.
Also, anchor that long neck with thick enough gauge wire and anchor extra carefully(strong) to the body form...so as not to break free with movement when dry.
Below are two blog posts detailing my process/learning experience with Rhea chicks including photos, maybe they will help you?https://kimberlybunting.wordpress.com/2015/03/10/the-greater-rhea-posse/https://kimberlybunting.wordpress.com/2017/04/26/real-vs-artificial/