When they hatch the chicks absorb the yolk. They can live off of that yolk for 72 hours or more. That way they can wait for the later ones to hatch before the broody hen has to take them off of the nest for food and water. If I see an emergency in the incubator where I need to take action I will open the incubator and deal with the emergency but in the vast majority of my hatches I wait until the hatch is over before I take any out. I don't want the humidity in the incubator to escape while the others are hatching.
It looks like your brooder is in your air conditioned house so the temperature is pretty constant. Do not use a heat lamp, that heat plate should work well. Inside your house a heat lamp is likely to overheat your chicks as it is harder to keep one area of the brooder cooler. If you are brooding outdoors and can set up a brooder where the heat lamp heats one area but other parts of the brooder can cool off a heat lamp can be very useful.
I assume it is one of those wire crates, not one pretty much enclosed in plastic. Will it be indoors or outdoors where the wind can hit it. Indoors you probably won't have enough of a breeze where you have to block the sides but it will not hurt. Outside you do not want a breeze hitting the chicks. I'd block it about 12" high, 18" at the most. I'd leave the top open so they have good ventilation.
