It's not a direct trade-off. You
can replace your airstones with waterfalls, as the method of adding dissolved oxygen to the water, but you still have to have a way of getting that
DO through the roots. Roots not getting oxygen will cause a lot of major issues, which is why it takes a lot of force to get to the denser parts.
As far as adding waterfalls to each tote, it's overkill. Adding a single waterfall, with a foot of drilled PVC to spray it, will add all the DO you'll need.
If you run an RDWC, you can get yourself a smallish 500gph pump to circulate all the water. I keep around 55-gallons in mine, and use a $25 450gph water pump.
68 to 70 degree water helps me to go a full grow with no flushes, keep white roots with no additives, keep the water from smelling, and helps me prevent root rot and slime. I wouldn't bother dropping below 66 degrees. And, if you can avoid a chiller, it's so worth it. They're expensive.
Take a look at my thread if you want to see how I did mine.
Thread