Welcome to BYC and best of luck with your first flock! You are getting a good start in disease prevention by ordering from a hatchery. One of the most common disease to watch out for in chicks is coccidiosis, which is treatable but must be caught quickly, so you might consider having Corid (amprolium) on hand. Also check whether or not your chicks are vaccinated for coccidiosis before deciding on medicated vs. non-medicated feed.
Many diseases can come from wild birds and other things in the environment, so it's not always possible to prevent, but by taking time to observe your chickens each day, you'll know something is wrong quickly and have the best chance of a good outcome.