On the chiller ... I don't use one, but I keep my tank in the basement, no direct light, and use LEDs to keep heat down.
On the rock/sand ... there are rules of thumb out there, but comes down to two things. What kind of look are you going for (open vs reef) and what kind of filtration system are you going for (heavy bio or heavy mechanical). Your answers to those questions will help dial in on the amount of rock/sand. In my tank, I wanted a reef tank mainly using bio filtration. Therefore, my tank has 300 lbs rock and 175 lbs sand.