Don't sweat the temp drop. Tilapia are hardy as long as they are in good health, and you bring them back up slowly.
Mine go into the mid 50's during winter....I lose a few, but the bigger ones seem to be more tolerant. The books/other people state they can't survive that low, I would imagine this depends on variety/strain. Mine seem to do just fine, as long as they have been in good health/condition going into the winter.
Reduce your feedings during cool downs or cold spells. It takes longer for digestion, and otherwise will reduce water quality faster due to spoiling uneaten food.
You can't have too much air. Just the way it is. Regardless of species of fish...more air is better.
I have 3 extra air pumps on my wintering over system. Don't need them, but have them anyway. Cold water also holds more DO than warm water.