At that temperature it's going to be more of a specialized tank so you'll have to be careful what you decide to put in there, sounds like maybe you already know that. 72 is going to be right at the edge where some coral are just going to be "hard doing" in those conditions. Also keep in mind it is going to slow things down in the tank, everything will run at a slower pace.
One other note on cooling a tank, a simple bank of fans blowing over the surface is very effective and far less costly than a chiller. I have a 250 gallon setup with a bank of 6 fans, even if the house is 80+ it'll cool it down below that number with a 78 degree target. I just mention this becuase chillers chew up power and add complexity where perhaps it isn't required?
As far as Oxygen, those would actually be at a maximum level if you had a thriving coral setup in the tank. Their photosynthetic process increases the oxygen level as a byproduct of growth. You will see if you had a pH controller that during the day the pH increases and at night it decreases like clockwork. This follows the decrease and increase of CO2 respectively. This is also why having a refugium with macroalgae is beneficial if you run the grow light at night, reduces the pH trough that you inevitable get in a tank.
