Welcome to BYC. Glad you decided to our flock. For sheer egg production, the best layers are White Leghorns (for white eggs) and Black and Red Sex Links (for brown eggs). These are the hens used by laying houses because they will both consistently churn out more than 300 eggs per hen per year. Other excellent layers are Australorps, Production Reds, Austra Whites, and California Whites, all of which occasionally lay over 300 eggs per hen per year. As Eggmachine11 pointed out, a Black Australorp holds the brown egg laying record with 364 eggs in 365 days although this is exceptional and not the norm. As long as your coop is well ventilated, they have plenty of shade, and plenty of cool, fresh water, all of these breeds and hybirds should be able to handle your southern Mississippi summers. Please feel free to ask any questions you may have. We are here to help in any way we can. Whatever breeds or hybrids you decide to get, good luck with your flock.